btrfs: raid56: remove redundant device check in rbio_add_io_page

The merging logic is always executed if the current stripe's device
is not missing. So there's no point in duplicating the check. Simply
remove it, while at it reduce the scope of the 'last_end' variable.
If the current stripe's device is missing we fail the stripe early on.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/raid56.c

@@ -1083,7 +1083,6 @@ static int rbio_add_io_page(struct btrfs_raid_bio *rbio,
 			    unsigned long bio_max_len)
 {
 	struct bio *last = bio_list->tail;
-	u64 last_end = 0;
 	int ret;
 	struct bio *bio;
 	struct btrfs_bio_stripe *stripe;
@@ -1098,15 +1097,14 @@ static int rbio_add_io_page(struct btrfs_raid_bio *rbio,
 
 	/* see if we can add this page onto our existing bio */
 	if (last) {
-		last_end = (u64)last->bi_iter.bi_sector << 9;
+		u64 last_end = (u64)last->bi_iter.bi_sector << 9;
 		last_end += last->bi_iter.bi_size;
 
 		/*
 		 * we can't merge these if they are from different
 		 * devices or if they are not contiguous
 		 */
-		if (last_end == disk_start && stripe->dev->bdev &&
-		    !last->bi_status &&
+		if (last_end == disk_start && !last->bi_status &&
 		    last->bi_disk == stripe->dev->bdev->bd_disk &&
 		    last->bi_partno == stripe->dev->bdev->bd_partno) {
 			ret = bio_add_page(last, page, PAGE_SIZE, 0);