[S390] Small barrier() and cpu_relax() cleanup.

cpu_relax() has barrier() semantics hence there is no need to use both
of them in conjunction in sclp_sync_wait(). Also change cpu_relax()
so it's more obvious that it has barrier semantics.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/include/asm-s390/processor.h b/include/asm-s390/processor.h
index cbbedc6..5dc6b93 100644
--- a/include/asm-s390/processor.h
+++ b/include/asm-s390/processor.h
@@ -201,9 +201,8 @@
 static inline void cpu_relax(void)
 {
 	if (MACHINE_HAS_DIAG44)
-		asm volatile("diag 0,0,68" : : : "memory");
-	else
-		barrier();
+		asm volatile("diag 0,0,68");
+	barrier();
 }
 
 /*