btrfs: use scrub_pause_on/off() to reduce code in scrub_enumerate_chunks()

Use new intruduced scrub_pause_on/off() can make this code block
clean and more readable.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/scrub.c

@@ -3503,8 +3503,8 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 
 		wait_event(sctx->list_wait,
 			   atomic_read(&sctx->bios_in_flight) == 0);
-		atomic_inc(&fs_info->scrubs_paused);
-		wake_up(&fs_info->scrub_pause_wait);
+
+		scrub_pause_on(fs_info);
 
 		/*
 		 * must be called before we decrease @scrub_paused.
@@ -3515,11 +3515,7 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 			   atomic_read(&sctx->workers_pending) == 0);
 		atomic_set(&sctx->wr_ctx.flush_all_writes, 0);
 
-		mutex_lock(&fs_info->scrub_lock);
-		__scrub_blocked_if_needed(fs_info);
-		atomic_dec(&fs_info->scrubs_paused);
-		mutex_unlock(&fs_info->scrub_lock);
-		wake_up(&fs_info->scrub_pause_wait);
+		scrub_pause_off(fs_info);
 
 		btrfs_put_block_group(cache);
 		if (ret)