Btrfs-progs: set return value to 0 if subvolume get-default successfully

cmd_subvol_get_default() returns 1 even if finds default subvolume
successfully.

Set the correct return value.

Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

cmds-subvolume.c

@@ -697,6 +697,7 @@ static int cmd_subvol_get_default(int argc, char **argv)
 	/* no need to resolve roots if FS_TREE is default */
 	if (default_id == BTRFS_FS_TREE_OBJECTID) {
 		printf("ID 5 (FS_TREE)\n");
+		ret = 0;
 		goto out;
 	}