btrfs: free ulist in qgroup_shared_accounting() error path

If tmp = ulist_alloc(GFP_NOFS) fails, we return without
freeing the previously allocated qgroups = ulist_alloc(GFP_NOFS)
and cause a memory leak.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index cf5aead..98cb6b2 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1798,8 +1798,10 @@
 		return -ENOMEM;
 
 	tmp = ulist_alloc(GFP_NOFS);
-	if (!tmp)
+	if (!tmp) {
+		ulist_free(qgroups);
 		return -ENOMEM;
+	}
 
 	btrfs_get_tree_mod_seq(fs_info, &elem);
 	ret = btrfs_find_all_roots(trans, fs_info, oper->bytenr, elem.seq,