s390/setup: use memblock_free_late() to free old stack

Use memblock_free_late() to free the old machine check stack to the
buddy allocator instead of leaking it.

Fixes: b61b1595 ("s390: add stack for machine check handler")
Cc: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: NSven Schnelle <svens@linux.ibm.com>
Signed-off-by: NHeiko Carstens <hca@linux.ibm.com>

arch/s390/kernel/setup.c

@@ -354,7 +354,7 @@ static int __init stack_realloc(void)
 	if (!new)
 		panic("Couldn't allocate machine check stack");
 	WRITE_ONCE(S390_lowcore.mcck_stack, new + STACK_INIT_OFFSET);
-	memblock_free(old, THREAD_SIZE);
+	memblock_free_late(old, THREAD_SIZE);
 	return 0;
 }
 early_initcall(stack_realloc);