mmc: bcm2835: fix potential null pointer dereferences

Null check at line 1165: if (mrq->cmd), implies that mrq->cmd might
be NULL.
Add null checks before dereferencing pointer mrq->cmd in order to avoid
any potential NULL pointer dereference.

Addresses-Coverity-ID: 1408740
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/bcm2835.c

@@ -1172,7 +1172,10 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
 	if (mrq->data && !is_power_of_2(mrq->data->blksz)) {
 		dev_err(dev, "unsupported block size (%d bytes)\n",
 			mrq->data->blksz);
+
+		if (mrq->cmd)
 			mrq->cmd->error = -EINVAL;
+
 		mmc_request_done(mmc, mrq);
 		return;
 	}
@@ -1194,7 +1197,10 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
 			readl(host->ioaddr + SDCMD) & SDCMD_CMD_MASK,
 			edm);
 		bcm2835_dumpregs(host);
+
+		if (mrq->cmd)
 			mrq->cmd->error = -EILSEQ;
+
 		bcm2835_finish_request(host);
 		mutex_unlock(&host->mutex);
 		return;
@@ -1207,7 +1213,7 @@ static void bcm2835_request(struct mmc_host *mmc, struct mmc_request *mrq)
 			if (!host->use_busy)
 				bcm2835_finish_command(host);
 		}
-	} else if (bcm2835_send_command(host, mrq->cmd)) {
+	} else if (mrq->cmd && bcm2835_send_command(host, mrq->cmd)) {
 		if (host->data && host->dma_desc) {
 			/* DMA transfer starts now, PIO starts after irq */
 			bcm2835_start_dma(host);