driver/rtc/class.c: check the error after rtc_read_time()

In rtc_suspend() and rtc_resume(), the error after rtc_read_time() is not
checked. If rtc device fail to read time, we cannot guarantee the
following process.

Add the verification code for returned rtc_read_time() error.

Signed-off-by: Hyogi Gim <[e-mail]>
Cc: Alessandro Zummo <[e-mail]>
Cc: "Rafael J. Wysocki" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/rtc/class.c

···
 	struct rtc_device	*rtc = to_rtc_device(dev);
 	struct rtc_time		tm;
 	struct timespec		delta, delta_delta;
+	int err;
 
 	if (has_persistent_clock())
 		return 0;
···
 		return 0;
 
 	/* snapshot the current RTC and system time at suspend*/
-	rtc_read_time(rtc, &tm);
+	err = rtc_read_time(rtc, &tm);
+	if (err < 0) {
+		pr_debug("%s:  fail to read rtc time\n", dev_name(&rtc->dev));
+		return 0;
+	}
+
 	getnstimeofday(&old_system);
 	rtc_tm_to_time(&tm, &old_rtc.tv_sec);
 
···
 	struct rtc_time		tm;
 	struct timespec		new_system, new_rtc;
 	struct timespec		sleep_time;
+	int err;
 
 	if (has_persistent_clock())
 		return 0;
···
 
 	/* snapshot the current rtc and system time at resume */
 	getnstimeofday(&new_system);
-	rtc_read_time(rtc, &tm);
+	err = rtc_read_time(rtc, &tm);
+	if (err < 0) {
+		pr_debug("%s:  fail to read rtc time\n", dev_name(&rtc->dev));
+		return 0;
+	}
+
 	if (rtc_valid_tm(&tm) != 0) {
 		pr_debug("%s:  bogus resume time\n", dev_name(&rtc->dev));
 		return 0;