Btrfs: switch to btrfs_previous_extent_item()

Since we have introduced btrfs_previous_extent_item() to search previous
extent item, just switch into it.
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Reviewed-by: Filipe Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/backref.c

@@ -1325,38 +1325,13 @@ int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
 	if (ret < 0)
 		return ret;
 
-	while (1) {
-		u32 nritems;
-		if (path->slots[0] == 0) {
-			btrfs_set_path_blocking(path);
-			ret = btrfs_prev_leaf(fs_info->extent_root, path);
-			if (ret != 0) {
-				if (ret > 0) {
-					pr_debug("logical %llu is not within "
-						 "any extent\n", logical);
-					ret = -ENOENT;
-				}
-				return ret;
-			}
-		} else {
-			path->slots[0]--;
-		}
-		nritems = btrfs_header_nritems(path->nodes[0]);
-		if (nritems == 0) {
-			pr_debug("logical %llu is not within any extent\n",
-				 logical);
-			return -ENOENT;
-		}
-		if (path->slots[0] == nritems)
-			path->slots[0]--;
-
-		btrfs_item_key_to_cpu(path->nodes[0], found_key,
-				      path->slots[0]);
-		if (found_key->type == BTRFS_EXTENT_ITEM_KEY ||
-		    found_key->type == BTRFS_METADATA_ITEM_KEY)
-			break;
+	ret = btrfs_previous_extent_item(fs_info->extent_root, path, 0);
+	if (ret) {
+		if (ret > 0)
+			ret = -ENOENT;
+		return ret;
 	}
-
+	btrfs_item_key_to_cpu(path->nodes[0], found_key, path->slots[0]);
 	if (found_key->type == BTRFS_METADATA_ITEM_KEY)
 		size = fs_info->extent_root->leafsize;
 	else if (found_key->type == BTRFS_EXTENT_ITEM_KEY)