Btrfs: fix typo in log message when starting a balance

The recent change titled "Btrfs: Check metadata redundancy on balance"
(already in linux-next) left a typo in a message for users:
metatdata -> metadata.
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/volumes.c

@@ -3752,7 +3752,7 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
 	if (btrfs_get_num_tolerated_disk_barrier_failures(bctl->meta.target) <
 		btrfs_get_num_tolerated_disk_barrier_failures(bctl->data.target)) {
 		btrfs_warn(fs_info,
-	"metatdata profile 0x%llx has lower redundancy than data profile 0x%llx",
+	"metadata profile 0x%llx has lower redundancy than data profile 0x%llx",
 			bctl->meta.target, bctl->data.target);
 	}