rtc: hym8563: fix invalid year calculation

Year field must be in BCD format, according to
hym8563 datasheet.

Due to the bug year 2016 became 2010.

Fixes: dcaf0384

 ("rtc: add hym8563 rtc-driver")
Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>