block: kill request ->cpu member

This was used for completion placement for the legacy path,
but for mq we have rq->mq_ctx->cpu for that. Add a helper
to get the request CPU assignment, as the mq_ctx type is
private to blk-mq.

Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
index 4ea9f2b..29dfd1b 100644
--- a/drivers/scsi/qla2xxx/qla_os.c
+++ b/drivers/scsi/qla2xxx/qla_os.c
@@ -1460,7 +1460,7 @@ __qla2xxx_eh_generic_reset(char *name, enum nexus_wait_type type,
 		goto eh_reset_failed;
 	}
 	err = 2;
-	if (do_reset(fcport, cmd->device->lun, cmd->request->cpu + 1)
+	if (do_reset(fcport, cmd->device->lun, blk_mq_rq_cpu(cmd->request) + 1)
 		!= QLA_SUCCESS) {
 		ql_log(ql_log_warn, vha, 0x800c,
 		    "do_reset failed for cmd=%p.\n", cmd);