hw/ppc/prep: use TYPE_MC146818_RTC instead of a hardcoded string

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190505152839.18650-2-philmd@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/hw/ppc/prep.c b/hw/ppc/prep.c
index b7f459d..ebee321 100644
--- a/hw/ppc/prep.c
+++ b/hw/ppc/prep.c
@@ -601,7 +601,7 @@
     uint16_t checksum = *(uint16_t *)opaque;
     ISADevice *rtc;
 
-    if (object_dynamic_cast(OBJECT(dev), "mc146818rtc")) {
+    if (object_dynamic_cast(OBJECT(dev), TYPE_MC146818_RTC)) {
         rtc = ISA_DEVICE(dev);
         rtc_set_memory(rtc, 0x2e, checksum & 0xff);
         rtc_set_memory(rtc, 0x3e, checksum & 0xff);