[S390] Convert to smp_call_function_single.

smp_call_function_single now has the same semantics as s390's
smp_call_function_on. Therefore convert to the *single variant
and get rid of some architecture specific code.

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/vtime.c b/arch/s390/kernel/vtime.c
index b6ed143..84ff78d 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -415,7 +415,7 @@
 
 /*
  * If we change a pending timer the function must be called on the CPU
- * where the timer is running on, e.g. by smp_call_function_on()
+ * where the timer is running on, e.g. by smp_call_function_single()
  *
  * The original mod_timer adds the timer if it is not pending. For compatibility
  * we do the same. The timer will be added on the current CPU as a oneshot timer.