platform/x86: amd-pmc: fix compilation without CONFIG_RTC_SYSTOHC_DEVICE

Just hardcode the RTC to "rtc0" which is the default for
CONFIG_RTC_SYSTOHC_DEVICE and used by all standard x86 distros.

Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Suggested-by: Hans de Goede <hdegoede@redhat.com>
Fixes: 59348401 ("platform/x86: amd-pmc: Add special handling for timer based S0i3 wakeup")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20211026171443.289-1-mario.limonciello@amd.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/amd-pmc.c

@@ -425,7 +425,7 @@ static int amd_pmc_verify_czn_rtc(struct amd_pmc_dev *pdev, u32 *arg)
 	if (pdev->major < 64 || (pdev->major == 64 && pdev->minor < 53))
 		return 0;
 
-	rtc_device = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
+	rtc_device = rtc_class_open("rtc0");
 	if (!rtc_device)
 		return 0;
 	rc = rtc_read_alarm(rtc_device, &alarm);