rtc: introduce lock helpers

Introduce rtc_lock and rtc_unlock to shorten the code when locking and
unlocking ops_lock from drivers.

Link: https://lore.kernel.org/r/20191019205034.6382-1-alexandre.belloni@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

include/linux/rtc.h

@@ -159,6 +159,9 @@ struct rtc_device {
 };
 #define to_rtc_device(d) container_of(d, struct rtc_device, dev)
 
+#define rtc_lock(d) mutex_lock(&d->ops_lock)
+#define rtc_unlock(d) mutex_unlock(&d->ops_lock)
+
 /* useful timestamps */
 #define RTC_TIMESTAMP_BEGIN_0000	-62167219200ULL /* 0000-01-01 00:00:00 */
 #define RTC_TIMESTAMP_BEGIN_1900	-2208988800LL /* 1900-01-01 00:00:00 */