rtc: use ktime_get_real_ts64() instead of getnstimeofday64()

getnstimeofday64() is just a wrapper around the ktime accessor, so
we should use that directly.

I considered using ktime_get_boottime_ts64() (to avoid leap second
problems) or ktime_get_real_seconds() (to simplify the calculation,
but in the end concluded that the existing interface is probably
the most appropriate in this case.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/class.c

@@ -68,7 +68,7 @@ static int rtc_suspend(struct device *dev)
 		return 0;
 	}
 
-	getnstimeofday64(&old_system);
+	ktime_get_real_ts64(&old_system);
 	old_rtc.tv_sec = rtc_tm_to_time64(&tm);
 
 
@@ -110,7 +110,7 @@ static int rtc_resume(struct device *dev)
 		return 0;
 
 	/* snapshot the current rtc and system time at resume */
-	getnstimeofday64(&new_system);
+	ktime_get_real_ts64(&new_system);
 	err = rtc_read_time(rtc, &tm);
 	if (err < 0) {
 		pr_debug("%s:  fail to read rtc time\n", dev_name(&rtc->dev));