target: iblock_execute_sync_cache() should use bio_set_op_attrs()

The original commit missed this function, it needs to mark it a
write flush.

Cc: Mike Christie <mchristi@redhat.com>
Fixes: e742fc32fcb4 ("target: use bio op accessors")
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/target/target_core_iblock.c

@@ -388,7 +388,7 @@ iblock_execute_sync_cache(struct se_cmd *cmd)
 	bio = bio_alloc(GFP_KERNEL, 0);
 	bio->bi_end_io = iblock_end_io_flush;
 	bio->bi_bdev = ib_dev->ibd_bd;
-	bio->bi_rw = WRITE_FLUSH;
+	bio_set_op_attrs(bio, REQ_OP_WRITE, WRITE_FLUSH);
 	if (!immed)
 		bio->bi_private = cmd;
 	submit_bio(bio);