md/raid1: remove unused bio in sync_request_write

The "bio" is not used in sync_request_write after commit a68e5870
("md/raid1: split out two sub-functions from sync_request_write").
Signed-off-by: NGuoqing Jiang <gqjiang@suse.com>
Signed-off-by: NShaohua Li <shli@fb.com>

drivers/md/raid1.c

@@ -2171,9 +2171,7 @@ static void sync_request_write(struct mddev *mddev, struct r1bio *r1_bio)
 	struct r1conf *conf = mddev->private;
 	int i;
 	int disks = conf->raid_disks * 2;
-	struct bio *bio, *wbio;
-
-	bio = r1_bio->bios[r1_bio->read_disk];
+	struct bio *wbio;
 
 	if (!test_bit(R1BIO_Uptodate, &r1_bio->state))
 		/* ouch - failed to read all of that. */