[GFS2] fix bz 231369, gfs2 will oops if you specify an invalid mount option

If you specify an invalid mount option when trying to mount a gfs2 filesystem,
gfs2 will oops.  The attached patch resolves this problem.

Signed-off-by: Josef Whiter <jwhiter@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 9f203ef..a3a24f2 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -2217,7 +2217,7 @@
 
 void gfs2_delete_debugfs_file(struct gfs2_sbd *sdp)
 {
-	if (sdp->debugfs_dentry)
+	if (sdp && sdp->debugfs_dentry)
 		debugfs_remove(sdp->debugfs_dentry);
 }