rtc: rtc-mc146818-lib: Use is_leap_year instead of calculate leap years

The is_leap_year() for determining leap year is provided in rtc lib.
This uses is_leap_year() instead of its own leap year determination
routine.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Acked-by: Maciej W. Rozycki <macro@orcam.me.uk>
Link: https://lore.kernel.org/r/20241007233618.1442937-1-nobuhiro1.iwamatsu@toshiba.co.jp
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Author: iwamatsu

drivers/rtc/rtc-mc146818-lib.c

@@ -216,7 +216,7 @@ int mc146818_set_time(struct rtc_time *time)
 	unsigned char save_control, save_freq_select;
 	unsigned int yrs;
 #ifdef CONFIG_MACH_DECSTATION
-	unsigned int real_yrs, leap_yr;
+	unsigned int real_yrs;
 #endif
 	unsigned char century = 0;
 
@@ -232,16 +232,14 @@ int mc146818_set_time(struct rtc_time *time)
 
 #ifdef CONFIG_MACH_DECSTATION
 	real_yrs = yrs;
-	leap_yr = ((!((yrs + 1900) % 4) && ((yrs + 1900) % 100)) ||
-			!((yrs + 1900) % 400));
 	yrs = 72;
 
 	/*
 	 * We want to keep the year set to 73 until March
 	 * for non-leap years, so that Feb, 29th is handled
 	 * correctly.
 	 */
-	if (!leap_yr && mon < 3) {
+	if (!is_leap_year(real_yrs + 1900) && mon < 3) {
 		real_yrs--;
 		yrs = 73;
 	}