btrfs-progs: restore: fix wrong return value if it fails to read specified fs root

Steps to reproduce:
 # mkfs.btrfs -f /dev/sda9
 # btrfs restore -f 1 -o /tmp /dev/sda9
 # echo $?

Fix to return 1 in this failure path.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

cmds-restore.c

@@ -1239,6 +1239,7 @@ int cmd_restore(int argc, char **argv)
 		root->node = read_tree_block(root, fs_location, root->leafsize, 0);
 		if (!root->node) {
 			fprintf(stderr, "Failed to read fs location\n");
+			ret = 1;
 			goto out;
 		}
 	}