scsi: sym53c8xx: fix NULL pointer dereference panic in sym_int_sir()

sym_int_sir() in sym_hipd.c does not check the command pointer for NULL before
using it in debug message prints.
Suggested-by: Matthew Wilcox <matthew.wilcox@oracle.com>
Signed-off-by: George Kennedy <george.kennedy@oracle.com>
Reviewed-by: Mark Kanda <mark.kanda@oracle.com>
Acked-by: Matthew Wilcox <matthew.wilcox@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sym53c8xx_2/sym_hipd.c

@@ -4370,6 +4370,13 @@ static void sym_nego_rejected(struct sym_hcb *np, struct sym_tcb *tp, struct sym
 	OUTB(np, HS_PRT, HS_BUSY);
 }
 
+#define sym_printk(lvl, tp, cp, fmt, v...) do { \
+	if (cp)							\
+		scmd_printk(lvl, cp->cmd, fmt, ##v);		\
+	else							\
+		starget_printk(lvl, tp->starget, fmt, ##v);	\
+} while (0)
+
 /*
  *  chip exception handler for programmed interrupts.
  */
@@ -4415,7 +4422,7 @@ static void sym_int_sir(struct sym_hcb *np)
 	 *  been selected with ATN.  We do not want to handle that.
 	 */
 	case SIR_SEL_ATN_NO_MSG_OUT:
-		scmd_printk(KERN_WARNING, cp->cmd,
+		sym_printk(KERN_WARNING, tp, cp,
 				"No MSG OUT phase after selection with ATN\n");
 		goto out_stuck;
 	/*
@@ -4423,7 +4430,7 @@ static void sym_int_sir(struct sym_hcb *np)
 	 *  having reselected the initiator.
 	 */
 	case SIR_RESEL_NO_MSG_IN:
-		scmd_printk(KERN_WARNING, cp->cmd,
+		sym_printk(KERN_WARNING, tp, cp,
 				"No MSG IN phase after reselection\n");
 		goto out_stuck;
 	/*
@@ -4431,7 +4438,7 @@ static void sym_int_sir(struct sym_hcb *np)
 	 *  an IDENTIFY.
 	 */
 	case SIR_RESEL_NO_IDENTIFY:
-		scmd_printk(KERN_WARNING, cp->cmd,
+		sym_printk(KERN_WARNING, tp, cp,
 				"No IDENTIFY after reselection\n");
 		goto out_stuck;
 	/*
@@ -4460,7 +4467,7 @@ static void sym_int_sir(struct sym_hcb *np)
 	case SIR_RESEL_ABORTED:
 		np->lastmsg = np->msgout[0];
 		np->msgout[0] = M_NOOP;
-		scmd_printk(KERN_WARNING, cp->cmd,
+		sym_printk(KERN_WARNING, tp, cp,
 			"message %x sent on bad reselection\n", np->lastmsg);
 		goto out;
 	/*