scsi: myrs: Fix dma_alloc_coherent() error check

Check for NULL return value with dma_alloc_coherent(), because DMA
address is not always set by dma_alloc_coherent() on failure.

Fixes: 77266186397c ("scsi: myrs: Add Mylex RAID controller (SCSI interface)")
Signed-off-by: Thomas Fourier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/myrs.c

···
 	/* Temporary dma mapping, used only in the scope of this function */
 	mbox = dma_alloc_coherent(&pdev->dev, sizeof(union myrs_cmd_mbox),
 				  &mbox_addr, GFP_KERNEL);
-	if (dma_mapping_error(&pdev->dev, mbox_addr))
+	if (!mbox)
 		return false;
 
 	/* These are the base addresses for the command memory mailbox array */
 	cs->cmd_mbox_size = MYRS_MAX_CMD_MBOX * sizeof(union myrs_cmd_mbox);
 	cmd_mbox = dma_alloc_coherent(&pdev->dev, cs->cmd_mbox_size,
 				      &cs->cmd_mbox_addr, GFP_KERNEL);
-	if (dma_mapping_error(&pdev->dev, cs->cmd_mbox_addr)) {
+	if (!cmd_mbox) {
 		dev_err(&pdev->dev, "Failed to map command mailbox\n");
 		goto out_free;
 	}
···
 	cs->stat_mbox_size = MYRS_MAX_STAT_MBOX * sizeof(struct myrs_stat_mbox);
 	stat_mbox = dma_alloc_coherent(&pdev->dev, cs->stat_mbox_size,
 				       &cs->stat_mbox_addr, GFP_KERNEL);
-	if (dma_mapping_error(&pdev->dev, cs->stat_mbox_addr)) {
+	if (!stat_mbox) {
 		dev_err(&pdev->dev, "Failed to map status mailbox\n");
 		goto out_free;
 	}
···
 	cs->fwstat_buf = dma_alloc_coherent(&pdev->dev,
 					    sizeof(struct myrs_fwstat),
 					    &cs->fwstat_addr, GFP_KERNEL);
-	if (dma_mapping_error(&pdev->dev, cs->fwstat_addr)) {
+	if (!cs->fwstat_buf) {
 		dev_err(&pdev->dev, "Failed to map firmware health buffer\n");
 		cs->fwstat_buf = NULL;
 		goto out_free;