lib/bpf: Fix and simplify bpf_mnt_check_target()

lib/bpf: Fix and simplify bpf_mnt_check_target()

As stated in commit ac3415f5c1b1 ("lib/fs: Fix and simplify make_path()"),
calling stat() before mkdir() is racey, because the entry might change in
between.

As the call to stat() seems to only check for target existence, we can
simply call mkdir() unconditionally and catch all errors but EEXIST.

Fixes: 95ae9a4870e7 ("bpf: fix mnt path when from env")
Signed-off-by: Andrea Claudi <aclaudi@redhat.com>