rtc: hym8563: Return -EINVAL if the time is known to be invalid

The current code returns -EPERM when the voltage loss bit is set.
Since the bit indicates that the time value is not valid, return
-EINVAL instead, which is the appropriate error code for this
situation.

Fixes: dcaf0384 ("rtc: add hym8563 rtc-driver")
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Link: https://lore.kernel.org/r/20191212153111.966923-1-paul.kocialkowski@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-hym8563.c

@@ -97,7 +97,7 @@ static int hym8563_rtc_read_time(struct device *dev, struct rtc_time *tm)
 
 	if (!hym8563->valid) {
 		dev_warn(&client->dev, "no valid clock/calendar values available\n");
-		return -EPERM;
+		return -EINVAL;
 	}
 
 	ret = i2c_smbus_read_i2c_block_data(client, HYM8563_SEC, 7, buf);