GFS2: Hash the negative dentry during inode lookup

Fix a regression introduced by:
6d4ade9 GFS2: Add atomic_open support
where an early return misses d_splice_alias() which had been
adding the negative dentry.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/inode.c

@@ -840,8 +840,10 @@ static struct dentry *__gfs2_lookup(struct inode *dir, struct dentry *dentry,
 	int error;
 
 	inode = gfs2_lookupi(dir, &dentry->d_name, 0);
-	if (!inode)
+	if (inode == NULL) {
+		d_add(dentry, NULL);
 		return NULL;
+	}
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);