drivers: rtc: fix null pointer access in armada38x_rtc_reset

Replace null pointer by pointer to device registers when calling
armada38x_rtc_write.

Signed-off-by: Francois Berder <fberder@outlook.fr>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/rtc/armada38x.c b/drivers/rtc/armada38x.c
index 2d264ac..2af64e3 100644
--- a/drivers/rtc/armada38x.c
+++ b/drivers/rtc/armada38x.c
@@ -121,7 +121,7 @@
 		armada38x_rtc_write(0, rtc, RTC_CONF_TEST);
 		mdelay(500);
 		armada38x_rtc_write(0, rtc, RTC_TIME);
-		armada38x_rtc_write(BIT(0) | BIT(1), 0, RTC_STATUS);
+		armada38x_rtc_write(BIT(0) | BIT(1), rtc, RTC_STATUS);
 	}
 
 	return 0;