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>