rtc: max77686: Use usleep_range() instead of msleep()

Documentation/timers/timers-howto.txt suggest to use usleep_range()
instead of msleep() for small msec (1ms - 20ms) since msleep() will
often sleep for 20ms for any value in that range.

This is fine in this case since 16ms is the _minimum_ delay required
by max77686 for an RTC update but by using usleep_range() instead of
msleep(), the driver can support other RTC IP blocks with a shorter
minimum delay (i.e: in the range of usecs instead of msecs).

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Andi Shyti <andi.shyti@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-max77686.c

@@ -41,7 +41,7 @@
 #define ALARM_ENABLE_SHIFT		7
 #define ALARM_ENABLE_MASK		(1 << ALARM_ENABLE_SHIFT)
 
-#define MAX77686_RTC_UPDATE_DELAY	16
+#define MAX77686_RTC_UPDATE_DELAY	16000
 
 enum {
 	RTC_SEC = 0,
@@ -130,7 +130,8 @@ static int max77686_rtc_update(struct max77686_rtc_info *info,
 				__func__, ret, data);
 	else {
 		/* Minimum 16ms delay required before RTC update. */
-		msleep(MAX77686_RTC_UPDATE_DELAY);
+		usleep_range(MAX77686_RTC_UPDATE_DELAY,
+			     MAX77686_RTC_UPDATE_DELAY * 2);
 	}
 
 	return ret;