s390/barrier: convert mb() to define again

Some of the now available common code drivers only compile if mb() is a define.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/barrier.h

@@ -13,15 +13,12 @@
  * to devices.
  */
 
-static inline void mb(void)
-{
 #ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
-	/* Fast-BCR without checkpoint synchronization */
-	asm volatile("bcr 14,0" : : : "memory");
+/* Fast-BCR without checkpoint synchronization */
+#define mb() do {  asm volatile("bcr 14,0" : : : "memory"); } while (0)
 #else
-	asm volatile("bcr 15,0" : : : "memory");
+#define mb() do {  asm volatile("bcr 15,0" : : : "memory"); } while (0)
 #endif
-}
 
 #define rmb()				mb()
 #define wmb()				mb()