rtc: stm32: migrate trace to log macro

Define LOG_CATEGORY to allow filtering with log command.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/rtc/stm32_rtc.c b/drivers/rtc/stm32_rtc.c
index f1d0ea9..1753283 100644
--- a/drivers/rtc/stm32_rtc.c
+++ b/drivers/rtc/stm32_rtc.c
@@ -2,6 +2,9 @@
 /*
  * Copyright (C) 2019, STMicroelectronics - All Rights Reserved
  */
+
+#define LOG_CATEGORY UCLASS_RTC
+
 #include <common.h>
 #include <clk.h>
 #include <dm.h>