drivers: rtc: off-by-one error in RV-8263-C8 driver

1. tm_mon in rtc_time structure has a range [0, 11],
while the RTC expects [1, 12]. Add missing
increasing / decreasing of this value.

2. Fix typo in debug log

Signed-off-by: Daniel Kampert <DanielKampert@kampis-elektroecke.de>