btrfs: do not BUG_ON() when dropping inode items from log root

When dropping inode items from a log tree at drop_inode_items(), we this
BUG_ON() on the result of btrfs_search_slot() because we don't expect an
exact match since having a key with an offset of (u64)-1 is unexpected.
That is generally true, but for dir index keys for example, we can get a
key with such an offset value, even though it's very unlikely and it would
take ages to increase the sequence counter for a dir index up to (u64)-1.
We can deal with an exact match, we just have to delete the key at that
slot, so there is really no need to BUG_ON(), error out or trigger any
warning. So remove the BUG_ON().
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -4056,14 +4056,14 @@ static int drop_inode_items(struct btrfs_trans_handle *trans,
 
 	while (1) {
 		ret = btrfs_search_slot(trans, log, &key, path, -1, 1);
-		BUG_ON(ret == 0); /* Logic error */
-		if (ret < 0)
-			break;
-
-		if (path->slots[0] == 0)
+		if (ret < 0) {
 			break;
+		} else if (ret > 0) {
+			if (path->slots[0] == 0)
+				break;
+			path->slots[0]--;
+		}
 
-		path->slots[0]--;
 		btrfs_item_key_to_cpu(path->nodes[0], &found_key,
 				      path->slots[0]);