btrfs: Separate scrub_blocked_if_needed() to scrub_pause_on/off()

It can reduce current duplicated code which is similar to
scrub_blocked_if_needed() but can not call it because little
different.
It also used by my next patch which is in same case.
Signed-off-by: NZhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/scrub.c

@@ -332,11 +332,14 @@ static void __scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
 	}
 }
 
-static void scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
+static void scrub_pause_on(struct btrfs_fs_info *fs_info)
 {
 	atomic_inc(&fs_info->scrubs_paused);
 	wake_up(&fs_info->scrub_pause_wait);
+}
 
+static void scrub_pause_off(struct btrfs_fs_info *fs_info)
+{
 	mutex_lock(&fs_info->scrub_lock);
 	__scrub_blocked_if_needed(fs_info);
 	atomic_dec(&fs_info->scrubs_paused);
@@ -345,6 +348,12 @@ static void scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
 	wake_up(&fs_info->scrub_pause_wait);
 }
 
+static void scrub_blocked_if_needed(struct btrfs_fs_info *fs_info)
+{
+	scrub_pause_on(fs_info);
+	scrub_pause_off(fs_info);
+}
+
 /*
  * used for workers that require transaction commits (i.e., for the
  * NOCOW case)