[S390] etr: fix compile error on !SMP

Since a5fbb6d1
"KVM: fix !SMP build error" smp_call_function isn't a define anymore
that folds into nothing but a define that calls up_smp_call_function
with all parameters. Hence we cannot #ifdef out the unused code
anymore...
This seems to be the preferred method, so do this for s390 as well.

arch/s390/kernel/time.c: In function 'etr_sync_clock':
arch/s390/kernel/time.c:825: error: 'clock_sync_cpu_start' undeclared
arch/s390/kernel/time.c:862: error: 'clock_sync_cpu_end' undeclared
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/time.c

@@ -744,7 +744,6 @@ static void etr_adjust_time(unsigned long long clock, unsigned long long delay)
 	}
 }
 
-#ifdef CONFIG_SMP
 static void etr_sync_cpu_start(void *dummy)
 {
 	int *in_sync = dummy;
@@ -777,7 +776,6 @@ static void etr_sync_cpu_start(void *dummy)
 static void etr_sync_cpu_end(void *dummy)
 {
 }
-#endif /* CONFIG_SMP */
 
 /*
  * Sync the TOD clock using the port refered to by aibp. This port