dm writecache: remove needless dereferences in __writecache_writeback_pmem()

bio is already available so there is no need to access it in terms of
the wb pointer.
Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-writecache.c

@@ -1478,9 +1478,9 @@ static void __writecache_writeback_pmem(struct dm_writecache *wc, struct writeba
 		bio = bio_alloc_bioset(GFP_NOIO, max_pages, &wc->bio_set);
 		wb = container_of(bio, struct writeback_struct, bio);
 		wb->wc = wc;
-		wb->bio.bi_end_io = writecache_writeback_endio;
-		bio_set_dev(&wb->bio, wc->dev->bdev);
-		wb->bio.bi_iter.bi_sector = read_original_sector(wc, e);
+		bio->bi_end_io = writecache_writeback_endio;
+		bio_set_dev(bio, wc->dev->bdev);
+		bio->bi_iter.bi_sector = read_original_sector(wc, e);
 		wb->page_offset = PAGE_SIZE;
 		if (max_pages <= WB_LIST_INLINE ||
 		    unlikely(!(wb->wc_list = kmalloc_array(max_pages, sizeof(struct wc_entry *),
@@ -1507,12 +1507,12 @@ static void __writecache_writeback_pmem(struct dm_writecache *wc, struct writeba
 			wb->wc_list[wb->wc_list_n++] = f;
 			e = f;
 		}
-		bio_set_op_attrs(&wb->bio, REQ_OP_WRITE, WC_MODE_FUA(wc) * REQ_FUA);
+		bio_set_op_attrs(bio, REQ_OP_WRITE, WC_MODE_FUA(wc) * REQ_FUA);
 		if (writecache_has_error(wc)) {
 			bio->bi_status = BLK_STS_IOERR;
-			bio_endio(&wb->bio);
+			bio_endio(bio);
 		} else {
-			submit_bio(&wb->bio);
+			submit_bio(bio);
 		}
 
 		__writeback_throttle(wc, wbl);