btrfs: Refactor transaction handling in received subvolume ioctl

If btrfs_transaction_commit fails it will proceed to call
cleanup_transaction, which in turn already does btrfs_abort_transaction.
So let's remove the unnecessary code duplication. Also let's be explicit
about handling failure of btrfs_uuid_tree_add by calling
btrfs_end_transaction.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>