rtc: use rtc_valid_tm() error code when reading date/time

There's a wrong comment in some RTC drivers that say it's better to ignore
rtc_valid_tm() when reading RTC timestamp. However this is wrong and is
better to return to the userspace the error if timestamp is not valid.

Signed-off-by: Andrea Scian <andrea.scian@dave.eu>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/drivers/rtc/rtc-isl12022.c b/drivers/rtc/rtc-isl12022.c
index f9b0827..3726271 100644
--- a/drivers/rtc/rtc-isl12022.c
+++ b/drivers/rtc/rtc-isl12022.c
@@ -151,12 +151,7 @@
 		tm->tm_sec, tm->tm_min, tm->tm_hour,
 		tm->tm_mday, tm->tm_mon, tm->tm_year, tm->tm_wday);
 
-	/* The clock can give out invalid datetime, but we cannot return
-	 * -EINVAL otherwise hwclock will refuse to set the time on bootup. */
-	if (rtc_valid_tm(tm) < 0)
-		dev_err(&client->dev, "retrieved date and time is invalid.\n");
-
-	return 0;
+	return rtc_valid_tm(tm);
 }
 
 static int isl12022_set_datetime(struct i2c_client *client, struct rtc_time *tm)