ppc64: memset destination if access_ok fails in copy_from_user

include/asm-ppc64/uaccess.h

@@ -273,6 +273,8 @@ copy_from_user(void *to, const void *from, unsigned long n)
 {
 	if (likely(access_ok(VERIFY_READ, from, n)))
 		n = __copy_from_user(to, from, n);
+	else
+		memset(to, 0, n);
 	return n;
 }