[S390] nohz: optimize arch_needs_cpu()

arch_needs_cpu() gets always executed on the current cpu. Therefore
the cpu parameter can be ignored it is possible to use __get_cpu_var()
instead of per_cpu() to access the per_cpu variable, which will
generate better code.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/cputime.h

@@ -202,7 +202,7 @@ static inline void s390_idle_check(struct pt_regs *regs, __u64 int_clock,
 
 static inline int s390_nohz_delay(int cpu)
 {
-	return per_cpu(s390_idle, cpu).nohz_delay != 0;
+	return __get_cpu_var(s390_idle).nohz_delay != 0;
 }
 
 #define arch_needs_cpu(cpu) s390_nohz_delay(cpu)