md/md-linear: enable io accounting

use md_account_bio() to enable io accounting, also make sure
mddev_suspend() will wait for all io to be done.

Signed-off-by: Yu Kuai <[e-mail]>
Reviewed-by: Xiao Ni <[e-mail]>
Signed-off-by: Song Liu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/md/md-linear.c

···
 		bio = split;
 	}
 
+	md_account_bio(mddev, &bio);
 	bio_set_dev(bio, tmp_dev->rdev->bdev);
 	bio->bi_iter.bi_sector = bio->bi_iter.bi_sector -
 		start_sector + data_offset;