s390/mm: disable KSM for storage key enabled pages

When storage keys are enabled unmerge already merged pages and prevent
new pages from being merged.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index df2e7f1..00d4607 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1751,7 +1751,7 @@
 extern int vmem_add_mapping(unsigned long start, unsigned long size);
 extern int vmem_remove_mapping(unsigned long start, unsigned long size);
 extern int s390_enable_sie(void);
-extern void s390_enable_skey(void);
+extern int s390_enable_skey(void);
 extern void s390_reset_cmma(struct mm_struct *mm);
 
 /*