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>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 37259ff..45ca8f9 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -582,8 +582,7 @@
 	if (start <= end && next_node) {
 		state = rb_entry(next_node, struct extent_state,
 				 rb_node);
-		if (state->start == start)
-			goto hit_next;
+		goto hit_next;
 	}
 	goto search_again;