filesslower crashes on kernel 5.8.0: cannot attach kprobe, probe entry may not exist

Somewhat similar to #3023

kernel-5.8.0-1.fc33.x86_64
bcc-tools-0.15.0-6.fc33.x86_64

```
# /usr/share/bcc/tools/fileslower
cannot attach kprobe, probe entry may not exist
Traceback (most recent call last):
File "/usr/share/bcc/tools/fileslower", line 202, in
b.attach_kprobe(event="__vfs_read", fn_name="trace_read_entry")
File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 676, in attach_kprobe
raise Exception("Failed to attach BPF program %s to kprobe %s" %
Exception: Failed to attach BPF program b'trace_read_entry' to kprobe b'__vfs_read'

# grep vfs_read /proc/kallsyms
ffffffff83323770 T vfs_read
ffffffff83324580 T vfs_readv
ffffffff83336e60 T vfs_readlink
ffffffff844caf40 r __ksymtab_vfs_readlink
ffffffff844e3462 r __kstrtabns_vfs_readlink
ffffffff844e65f7 r __kstrtab_vfs_readlink
```