md/raid5: use do_div() for 64 bit divisions in raid5_sync_request

We get compilation error on 32-bit architectures (e.g. m68k), as:

  ERROR: modpost: "__udivdi3" [drivers/md/raid456.ko] undefined!

Since 'sync_blocks' is defined as u64, use do_div() to fix this error.

Fixes: c911c46c ("md/raid456: convert macro STRIPE_* to RAID5_STRIPE_*")
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

drivers/md/raid5.c

@@ -6104,7 +6104,7 @@ static inline sector_t raid5_sync_request(struct mddev *mddev, sector_t sector_n
 	    !md_bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
 	    sync_blocks >= RAID5_STRIPE_SECTORS(conf)) {
 		/* we can skip this block, and probably more */
-		sync_blocks /= RAID5_STRIPE_SECTORS(conf);
+		do_div(sync_blocks, RAID5_STRIPE_SECTORS(conf));
 		*skipped = 1;
 		/* keep things rounded to whole stripes */
 		return sync_blocks * RAID5_STRIPE_SECTORS(conf);