rtc: ds1302: fix write value for day of week register

The valid range of day of week register for DS1302 is 1 to 7.  But the
set_time callback for rtc-ds1302 attempts to write the value of
tm->tm_wday which is in the range 0 to 6.  While the get_time callback
correctly decodes the register.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Sergey Yanovich <ynvich@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>