Incorrect data returned by pio_get_var for ADIOS type when IO root task rank is non-zero

Within a union communicator, IO tasks constitute a subset of compute
tasks, wherein the rank of the IO root task may not necessarily be 0.
For instance, in a scenario involving 16 compute tasks, IO tasks could
be designated as {1, 5, 9, 13}.

Under these circumstances, pio_get_var retrieves inaccurate data
specifically with ADIOS type (although it functions correctly with
PnetCDF type).

[Steps to reproduce]

First, check out latest scorpio master branch.
```
git clone https://github.com/E3SM-Project/scorpio.git
cd scorpio
```
Next, replace the content of examples/c/example1.c with the test code shown below.
```
#include
#include
#include
#ifdef TIMING
#include
#endif

#define NUM_NETCDF_FLAVORS 2

int main(int argc, char* argv[])
{
const int niotasks = 4;
const int ioproc_stride = 4;
const int ioproc_start = 1;
const int put_var_val = 42;

int rank;
int ntasks;
int format[NUM_NETCDF_FLAVORS];
int iosysid;
char filename[PIO_MAX_NAME];
int num_flavors = 0;
int ncid;
int varid;
int get_var_val;

#ifdef TIMING
GPTLinitialize();
#endif

MPI_Init(&argc, &argv);

MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &ntasks);

if (ntasks != 16)
{
if (rank == 0)
printf("This test must be run with exactly 16 MPI tasks!\n");

MPI_Finalize();

#ifdef TIMING
GPTLfinalize();
#endif

return -1;
}

PIOc_Init_Intracomm(MPI_COMM_WORLD, niotasks, ioproc_stride, ioproc_start, PIO_REARR_BOX, &iosysid);

#ifdef _PNETCDF
format[num_flavors++] = PIO_IOTYPE_PNETCDF;
#endif
#ifdef _ADIOS2
format[num_flavors++] = PIO_IOTYPE_ADIOS;
#endif

for (int fmt = 0; fmt < num_flavors; fmt++)
{
sprintf(filename, "test_get_var_%d.nc", fmt);

ncid = -1;
PIOc_createfile(iosysid, &ncid, &(format[fmt]), filename, PIO_CLOBBER);

varid = -1;
PIOc_def_var(ncid, "dummy_scalar_var", PIO_INT, 0, NULL, &varid);

PIOc_enddef(ncid);

PIOc_put_var_int(ncid, varid, &put_var_val);

PIOc_closefile(ncid);

ncid = -1;
PIOc_openfile(iosysid, &ncid, &(format[fmt]), filename, PIO_NOWRITE);

varid = -1;
PIOc_inq_varid(ncid, "dummy_scalar_var", &varid);

get_var_val = -1;
PIOc_get_var_int(ncid, varid, &get_var_val);

if (get_var_val != put_var_val)
printf("fmt = %d, rank = %d, pio_get_var returned wrong data, expected: %d actual: %d\n",
fmt, rank, put_var_val, get_var_val);

PIOc_closefile(ncid);
}

PIOc_finalize(iosysid);

MPI_Finalize();

#ifdef TIMING
GPTLfinalize();
#endif

return 0;
}
```
Then, build scorpio and run example1.
```
mkdir build
cd build

ADIOS2_DIR=/path/to/adios2/installation \
CC=mpicc CXX=mpicxx FC=mpifort cmake -Wno-dev \
-DWITH_ADIOS2=ON \
-DWITH_NETCDF=OFF \
-DPnetCDF_PATH=/path/to/pnetcdf/installation \
-DPIO_USE_MALLOC=ON \
-DPIO_ENABLE_EXAMPLES=ON \
..

make

cd examples/c

mpiexec -n 16 ./example1
```
Output is shown below.
```
fmt = 1, rank = 0, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 1, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 2, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 3, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 4, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 5, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 6, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 7, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 8, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 9, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 10, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 11, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 12, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 13, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 14, pio_get_var returned wrong data, expected: 42 actual: -1
fmt = 1, rank = 15, pio_get_var returned wrong data, expected: 42 actual: -1
```