btrfs: open code rbtree search in split_state

Preparatory work to remove tree_insert from extent_io.c, the rbtree
search loop is a known and simple so it can be open coded.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -607,7 +607,8 @@ static int insert_state(struct extent_io_tree *tree,
 static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
 		       struct extent_state *prealloc, u64 split)
 {
-	struct rb_node *node;
+	struct rb_node *parent = NULL;
+	struct rb_node **node;
 
 	if (tree->private_data && is_data_inode(tree->private_data))
 		btrfs_split_delalloc_extent(tree->private_data, orig, split);
@@ -617,12 +618,27 @@ static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
 	prealloc->state = orig->state;
 	orig->start = split;
 
-	node = tree_insert(&tree->state, &orig->rb_node, prealloc->end,
-			   &prealloc->rb_node, NULL, NULL);
-	if (node) {
+	parent = &orig->rb_node;
+	node = &parent;
+	while (*node) {
+		struct tree_entry *entry;
+
+		parent = *node;
+		entry = rb_entry(parent, struct tree_entry, rb_node);
+
+		if (prealloc->end < entry->start) {
+			node = &(*node)->rb_left;
+		} else if (prealloc->end > entry->end) {
+			node = &(*node)->rb_right;
+		} else {
 			free_extent_state(prealloc);
 			return -EEXIST;
 		}
+	}
+
+	rb_link_node(&prealloc->rb_node, parent, node);
+	rb_insert_color(&prealloc->rb_node, &tree->state);
+
 	return 0;
 }