mmc: core: Fix NULL ptr crash from mmc_should_fail_request

In case of CQHCI, mrq->cmd may be NULL for data requests (non DCMD).
In such case mmc_should_fail_request is directly dereferencing
mrq->cmd while cmd is NULL.
Fix this by checking for mrq->cmd pointer.

Fixes: 72a5af55 ("mmc: core: Add support for handling CQE requests")
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/core.c

@@ -95,7 +95,7 @@ static void mmc_should_fail_request(struct mmc_host *host,
 	if (!data)
 		return;
 
-	if (cmd->error || data->error ||
+	if ((cmd && cmd->error) || data->error ||
 	    !should_fail(&host->fail_mmc_request, data->blksz * data->blocks))
 		return;