rtc: mc146818: Add a comment to the #endif

Add a comment to make it clear to which block the #endif relates.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

drivers/rtc/mc146818.c

@@ -192,7 +192,7 @@ static void mc146818_init(void)
 	/* Clear any pending interrupts */
 	mc146818_read8(RTC_CONFIG_C);
 }
-#endif
+#endif /* CONFIG_CMD_DATE */
 
 #ifdef CONFIG_DM_RTC