rtc: em3027: correct month value

The RTC month value is 1-indexed, but the kernel assumes it is 0-indexed.
This may result in the RTC not rolling over correctly.

Signed-off-by: Ilya Ledvich <ilya@compulab.co.il>
Reviewed-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Link: https://lore.kernel.org/r/20191101095422.14787-1-ilya@compulab.co.il


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>