btrfs: remove pointless WARN_ON() in cache_save_setup()

This WARN_ON(ret) is never executed since the previous if statement makes
us jump into the 'out_put' label when ret is not zero. The existing
transaction abort inside the if statement also gives us a stack trace,
so we don't need to move the WARN_ON(ret) into the if statement either.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/block-group.c

@@ -3341,7 +3341,6 @@ static int cache_save_setup(struct btrfs_block_group *block_group,
 		btrfs_abort_transaction(trans, ret);
 		goto out_put;
 	}
-	WARN_ON(ret);
 
 	/* We've already setup this transaction, go ahead and exit */
 	if (block_group->cache_generation == trans->transid &&