rtc: rtc-mrst: Replace mdelay() with msleep() in mrst_read_time()

mrst_read_time() is never called in atomic context.
It calls mdelay() to busily wait, which is not necessary.
mdelay() can be replaced with msleep().

This is found by a static analysis tool named DCNS written by myself.
Signed-off-by: NJia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-mrst.c

@@ -90,7 +90,7 @@ static int mrst_read_time(struct device *dev, struct rtc_time *time)
 	unsigned long flags;
 
 	if (vrtc_is_updating())
-		mdelay(20);
+		msleep(20);
 
 	spin_lock_irqsave(&rtc_lock, flags);
 	time->tm_sec = vrtc_cmos_read(RTC_SECONDS);