[S390] Fix sparse warnings.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 78c8e55..d3cbfa3 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -172,7 +172,7 @@
 	show_registers(regs);
 	/* Show stack backtrace if pt_regs is from kernel mode */
 	if (!(regs->psw.mask & PSW_MASK_PSTATE))
-		show_trace(0,(unsigned long *) regs->gprs[15]);
+		show_trace(NULL, (unsigned long *) regs->gprs[15]);
 }
 
 extern void kernel_thread_starter(void);