KVM: s390: Cleanup usage of current->mm in set_guest_storage_key

In set_guest_storage_key, we really want to reference the mm struct given as
a parameter to the function. So replace the current->mm reference with the
mm struct passed in by the caller.
Signed-off-by: Jason J. Herne <jjherne@us.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/mm/pgtable.c

@@ -936,7 +936,7 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
 
 	down_read(&mm->mmap_sem);
 retry:
-	ptep = get_locked_pte(current->mm, addr, &ptl);
+	ptep = get_locked_pte(mm, addr, &ptl);
 	if (unlikely(!ptep)) {
 		up_read(&mm->mmap_sem);
 		return -EFAULT;