md/bitmap: revert a patch

This reverts commit 8031c3dd. That patches doesn't work well if PAGE_SIZE >
4k. We will fix the original problem with a different approach.

Fix: 8031c3dd(md/bitmap: copy correct data for bitmap super)
Reported-by: NJoshua Kinard <kumba@gentoo.org>
Cc: stable@vger.kernel.org (4.10+)
Suggested-by: NNeil Brown <neilb@suse.com>
Signed-off-by: NShaohua Li <shli@fb.com>

drivers/md/bitmap.c

@@ -625,7 +625,7 @@ static int bitmap_read_sb(struct bitmap *bitmap)
 		err = read_sb_page(bitmap->mddev,
 				   offset,
 				   sb_page,
-				   0, PAGE_SIZE);
+				   0, sizeof(bitmap_super_t));
 	}
 	if (err)
 		return err;
@@ -2123,7 +2123,7 @@ int bitmap_resize(struct bitmap *bitmap, sector_t blocks,
 	if (store.sb_page && bitmap->storage.sb_page)
 		memcpy(page_address(store.sb_page),
 		       page_address(bitmap->storage.sb_page),
-		       PAGE_SIZE);
+		       sizeof(bitmap_super_t));
 	bitmap_file_unmap(&bitmap->storage);
 	bitmap->storage = store;