potential cleanup of auto real conversions in chemsitry

Using `-Wconversion-extra` flag with GNU, noting potential places we could clean up

```
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/utils/mo_util.F90:214:17:

214 | if (u < 0.1) vs(j,i) = -vs(j,i)
| 1
Warning: Conversion from 'REAL(4)' to 'REAL(8)' at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/utils/mo_util.F90:214:17:

214 | if (u < 0.1) vs(j,i) = -vs(j,i)
| 1
Warning: Conversion from 'REAL(4)' to 'REAL(8)' at (1) [-Wconversion-extra]
```

```
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/utils/horizontal_interpolate.F90:50:15:

50 | lon2(i2) = (float(i2)-1.0_r8)*360.0_r8/float(im2)
| 1
Warning: Conversion from REAL(4) to REAL(8) at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/utils/horizontal_interpolate.F90:50:47:

50 | lon2(i2) = (float(i2)-1.0_r8)*360.0_r8/float(im2)
| 1
Warning: Conversion from REAL(4) to REAL(8) at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/utils/horizontal_interpolate.F90:53:52:

53 | lat2(j2) = -90.0_r8+(float(j2)-1.0_r8)*180.0_r8/(float(jm2)-1.0_r8)
| 1
Warning: Conversion from REAL(4) to REAL(8) at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/utils/horizontal_interpolate.F90:53:24:

53 | lat2(j2) = -90.0_r8+(float(j2)-1.0_r8)*180.0_r8/(float(jm2)-1.0_r8)
| 1
Warning: Conversion from REAL(4) to REAL(8) at (1) [-Wconversion-extra]
```

```
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/mo_schu.F90:12:47:

12 | real(r8), parameter :: t_del = 5._r8/(tdim-1)
| 1
Warning: Conversion from INTEGER(4) to REAL(8) at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/mo_schu.F90:13:41:

13 | real(r8), parameter :: t_fac = (tdim-1)/5._r8
| 1
Warning: Conversion from INTEGER(4) to REAL(8) at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/mo_schu.F90:148:30:

148 | col = 22._r8 + t_del*real(k-1)
| 1
Warning: Conversion from REAL(4) to REAL(8) at (1) [-Wconversion-extra]
```

```
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/apex_subs.F90:4222:56:

4222 | R2D=57.2957795130823208767981548147_r8)
| 1
Warning: Non-significant digits in 'REAL(8)' number at (1), maybe incorrect KIND [-Wconversion-extra]

/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/apex_subs.F90:4263:38:

4263 | L0 = -79.549_r8 + (-.238699_r8*(YR-4*NLEAP) + 3.08514E-2_r8*NLEAP)
| 1
Warning: Conversion from INTEGER(4) to REAL(8) at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/apex_subs.F90:4263:71:

4263 | L0 = -79.549_r8 + (-.238699_r8*(YR-4*NLEAP) + 3.08514E-2_r8*NLEAP)
| 1
Warning: Conversion from INTEGER(4) to REAL(8) at (1) [-Wconversion-extra]
....

```

```
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/UCI_fjx_sub_mod.f90:1159:36:

1159 | PL(I) = PL(I-1)*X*(2.d0-1.0/DEN) - PL(I-2)*(1.d0-1.d0/DEN)
| 1
Warning: Conversion from 'REAL(4)' to 'REAL(8)' at (1) [-Wconversion-extra]
```

```
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/UCI_fjx_sub_mod.f90:1700:62:

1700 | H(I,L1) = H(I,L1) -2.0d0*D2*C(I,L1) +SUM0*SURFAC*0.25*RFL(5)*ZFLUX
| 1
Warning: Conversion from 'REAL(4)' to 'REAL(8)' at (1) [-Wconversion-extra]
/global/cfs/cdirs/e3sm/ndk/repos/me24-aug15/components/eam/src/chemistry/mozart/UCI_fjx_sub_mod.f90:2037:21:

2037 | DD = 7.24e18*PP/TT
| 1
Warning: Conversion from 'REAL(4)' to 'REAL(8)' at (1) [-Wconversion-extra]
....
```