mmc: block: Fix tag condition with packed writes

Apparently a cut-and-paste error, 'do_data_tag' is using 'brq' for data
size even though 'brq' has not been set up. Instead use blk_rq_sectors().
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/card/block.c

@@ -1800,8 +1800,7 @@ static void mmc_blk_packed_hdr_wrq_prep(struct mmc_queue_req *mqrq,
 		do_data_tag = (card->ext_csd.data_tag_unit_size) &&
 			(prq->cmd_flags & REQ_META) &&
 			(rq_data_dir(prq) == WRITE) &&
-			((brq->data.blocks * brq->data.blksz) >=
-			 card->ext_csd.data_tag_unit_size);
+			blk_rq_bytes(prq) >= card->ext_csd.data_tag_unit_size;
 		/* Argument of CMD23 */
 		packed_cmd_hdr[(i * 2)] = cpu_to_le32(
 			(do_rel_wr ? MMC_CMD23_ARG_REL_WR : 0) |