kernel/arch/arm: fix missing return statement in rtc

Change-Id: Ib5a2e06884b6973ed102b30b1339a7b800c95418
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4781
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

src/system/kernel/arch/arm/arch_real_time_clock.cpp

@@ -18,13 +18,14 @@
 status_t
 arch_rtc_init(kernel_args *args, struct real_time_data *data)
 {
-	return B_OK;
+	return B_NOT_SUPPORTED;
 }
 
 
 uint32
 arch_rtc_get_hw_time(void)
 {
+	return 0;
 }