btrfs: Remove redundant WARN_ON in walk_down_log_tree

level <0 and level >= BTRFS_MAX_LEVEL are already performed upon
extent buffer read by tree checker in btrfs_check_node.
go. As far as 'level <= 0'  we are guaranteed that level is '> 0'
because the value of level _before_ reading 'next' is larger than 1
(otherwise we wouldn't have executed that code at all) this in turn
guarantees that 'level' after btrfs_read_buffer is 'level - 1' since
we verify this invariant in:

    btrfs_read_buffer
     btree_read_extent_buffer_pages
      btrfs_verify_level_key

This guarantees that level can never be '<= 0' so the warn on is
never triggered.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -2674,14 +2674,9 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
 	u32 blocksize;
 	int ret = 0;
 
-	WARN_ON(*level < 0);
-	WARN_ON(*level >= BTRFS_MAX_LEVEL);
-
 	while (*level > 0) {
 		struct btrfs_key first_key;
 
-		WARN_ON(*level < 0);
-		WARN_ON(*level >= BTRFS_MAX_LEVEL);
 		cur = path->nodes[*level];
 
 		WARN_ON(btrfs_header_level(cur) != *level);
@@ -2748,7 +2743,6 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
 			return ret;
 		}
 
-		WARN_ON(*level <= 0);
 		if (path->nodes[*level-1])
 			free_extent_buffer(path->nodes[*level-1]);
 		path->nodes[*level-1] = next;
@@ -2756,9 +2750,6 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
 		path->slots[*level] = 0;
 		cond_resched();
 	}
-	WARN_ON(*level < 0);
-	WARN_ON(*level >= BTRFS_MAX_LEVEL);
-
 	path->slots[*level] = btrfs_header_nritems(path->nodes[*level]);
 
 	cond_resched();