nfsd: fix comparison in fh_fsid_match()

We're supposed to be testing that the fh_fsid's match but because the
parenthesis are in the wrong place, then we only check the first
byte.

Fixes: 9558f250 ('nfsd: add fh_fsid_match helper')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>