s390: add uninitialized_var() to suppress false positive compiler warnings

Get rid of these:

arch/s390/kernel/smp.c:134:19: warning: ‘status’ may be used uninitialized in this function [-Wuninitialized]
arch/s390/mm/pgtable.c:641:10: warning: ‘table’ may be used uninitialized in this function [-Wuninitialized]
arch/s390/mm/pgtable.c:644:12: warning: ‘page’ may be used uninitialized in this function [-Wuninitialized]
drivers/s390/cio/cio.c:1037:14: warning: ‘schid’ may be used uninitialized in this function [-Wuninitialized]

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/smp.c b/arch/s390/kernel/smp.c
index 8676aab..ea431e5 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -126,7 +126,7 @@
 
 static inline int pcpu_stopped(struct pcpu *pcpu)
 {
-	u32 status;
+	u32 uninitialized_var(status);
 
 	if (__pcpu_sigp(pcpu->address, SIGP_SENSE,
 			0, &status) != SIGP_CC_STATUS_STORED)