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>

arch/s390/kernel/smp.c

@@ -126,7 +126,7 @@ static int pcpu_sigp_retry(struct pcpu *pcpu, u8 order, u32 parm)
 
 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)

arch/s390/mm/pgtable.c

@@ -609,8 +609,8 @@ static inline unsigned int atomic_xor_bits(atomic_t *v, unsigned int bits)
  */
 unsigned long *page_table_alloc(struct mm_struct *mm, unsigned long vmaddr)
 {
-	struct page *page;
-	unsigned long *table;
+	unsigned long *uninitialized_var(table);
+	struct page *uninitialized_var(page);
 	unsigned int mask, bit;
 
 	if (mm_has_pgste(mm))

drivers/s390/cio/cio.c

@@ -1029,7 +1029,7 @@ extern void do_reipl_asm(__u32 schid);
 /* Make sure all subchannels are quiet before we re-ipl an lpar. */
 void reipl_ccw_dev(struct ccw_dev_id *devid)
 {
-	struct subchannel_id schid;
+	struct subchannel_id uninitialized_var(schid);
 
 	s390_reset_system(NULL, NULL);
 	if (reipl_find_schid(devid, &schid) != 0)