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

Fixes: e01580bf9e ("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>

diff --git a/fs/gfs2/acl.c b/fs/gfs2/acl.c
index 3088e2a..7b31430 100644
--- a/fs/gfs2/acl.c
+++ b/fs/gfs2/acl.c
@@ -73,7 +73,7 @@
 
 	BUG_ON(name == NULL);
 
-	if (acl->a_count > GFS2_ACL_MAX_ENTRIES(GFS2_SB(inode)))
+	if (acl && acl->a_count > GFS2_ACL_MAX_ENTRIES(GFS2_SB(inode)))
 		return -E2BIG;
 
 	if (type == ACL_TYPE_ACCESS) {