drivers/rtc/rtc-pl031.c: configure correct wday for 2000-01-01
The reset date of the ST Micro version of PL031 is 2000-01-01. The
correct weekday for 2000-01-01 is saturday, but pl031 is initialized to
sunday. This may lead to alarm malfunction, so configure the correct
wday if RTC_DR indicates reset.