rtc+getdate: initialize tm_wday for mktime()

Even though mktime() is documented as ignoring the tm_wday field, the
coverity static analyzer complains about passing an uninitialized value.
Set the field to zero to make it happy.

getdate.y

@@ -943,6 +943,7 @@ get_date (const char *p, const time_t *now)
   tm.tm_hour += yyRelHour;
   tm.tm_min += yyRelMinutes;
   tm.tm_sec += yyRelSeconds;
+  tm.tm_wday = 0;
 
   /* Let mktime deduce tm_isdst if we have an absolute timestamp,
      or if the relative timestamp mentions days, months, or years.  */

rtc_linux.c

@@ -802,6 +802,7 @@ read_from_device(int fd_, int event, void *any)
     rtc_tm.tm_mday = rtc_raw.tm_mday;
     rtc_tm.tm_mon = rtc_raw.tm_mon;
     rtc_tm.tm_year = rtc_raw.tm_year;
+    rtc_tm.tm_wday = 0;
 
     rtc_t = t_from_rtc(&rtc_tm);