md: remove __clear_page_buffers and use attach/detach_page_private

After introduction attach/detach_page_private in pagemap.h, we can remove
the duplicated code and call the new functions.

Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Song Liu <song@kernel.org>
Link: http://lkml.kernel.org/r/20200517214718.468-3-guoqing.jiang@cloud.ionos.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/md-bitmap.c

@@ -324,14 +324,6 @@ static void end_bitmap_write(struct buffer_head *bh, int uptodate)
 		wake_up(&bitmap->write_wait);
 }
 
-/* copied from buffer.c */
-static void
-__clear_page_buffers(struct page *page)
-{
-	ClearPagePrivate(page);
-	set_page_private(page, 0);
-	put_page(page);
-}
 static void free_buffers(struct page *page)
 {
 	struct buffer_head *bh;
@@ -345,7 +337,7 @@ static void free_buffers(struct page *page)
 		free_buffer_head(bh);
 		bh = next;
 	}
-	__clear_page_buffers(page);
+	detach_page_private(page);
 	put_page(page);
 }
 
@@ -374,7 +366,7 @@ static int read_page(struct file *file, unsigned long index,
 		ret = -ENOMEM;
 		goto out;
 	}
-	attach_page_buffers(page, bh);
+	attach_page_private(page, bh);
 	blk_cur = index << (PAGE_SHIFT - inode->i_blkbits);
 	while (bh) {
 		block = blk_cur;