s390/kernel: use stnsm 255 instead of stosm 0

On some models, stnsm 255 might be slightly faster than stosm 0.
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/irqflags.h

@@ -36,7 +36,7 @@ static inline notrace void __arch_local_irq_ssm(unsigned long flags)
 
 static inline notrace unsigned long arch_local_save_flags(void)
 {
-	return __arch_local_irq_stosm(0x00);
+	return __arch_local_irq_stnsm(0xff);
 }
 
 static inline notrace unsigned long arch_local_irq_save(void)