GFS2: Fix crash during ACL deletion in acl max entry check in gfs2_set_acl()

commit 278702074ff77b1a3fa2061267997095959f5e2c upstream.

Fixes: e01580bf ("gfs2: use generic posix ACL infrastructure")
Reported-by: Eric Meddaugh <etmsys@rit.edu>
Tested-by: Eric Meddaugh <etmsys@rit.edu>
Signed-off-by: Andrew Elble <aweits@rit.edu>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>