scsi: mac53c94: Fix warning comparing pointer to 0

Fix the following coccicheck warning:

drivers/scsi/mac53c94.c:237:12-13: WARNING comparing pointer to 0

Link: https://lore.kernel.org/r/1647244711-31575-1-git-send-email-baihaowen@meizu.com
Signed-off-by: Haowen Bai <baihaowen@meizu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mac53c94.c

@@ -234,7 +234,7 @@ static void mac53c94_interrupt(int irq, void *dev_id)
 		++mac53c94_errors;
 		writeb(CMD_NOP + CMD_DMA_MODE, &regs->command);
 	}
-	if (cmd == 0) {
+	if (!cmd) {
 		printk(KERN_DEBUG "53c94: interrupt with no command active?\n");
 		return;
 	}