Btrfs: be less strict on finding next node in clear_extent_bit

In clear_extent_bit, it is enough that next node is adjacent in tree level.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>

fs/btrfs/extent_io.c

@@ -582,7 +582,6 @@ int clear_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
 	if (start <= end && next_node) {
 		state = rb_entry(next_node, struct extent_state,
 				 rb_node);
-		if (state->start == start)
 		goto hit_next;
 	}
 	goto search_again;