goldfish_rtc: Fix handling a local time RTC

The default QEMU config is to have the RTC in UTC. However, if run with
-rtc base=localtime (and wall_cmos_clock is set to match), the driver
fails to account for adjkerntz due to the use of CLOCKF_SETTIME_NO_ADJ.
Copy the same code used by other CLOCKF_SETTIME_NO_ADJ-using drivers
to fix this, namely manually subtracting utc_offset().

Fixes:		d63a631e72 ("Add Goldfish RTC device driver for RISC-V")
MFC after:	1 week

sys/dev/goldfish/goldfish_rtc.c

@@ -151,6 +151,11 @@ goldfish_rtc_settime(device_t dev, struct timespec *ts)
 
 	sc = device_get_softc(dev);
 
+	/*
+	 * We request a timespec with no resolution-adjustment.  That also
+	 * disables utc adjustment, so apply that ourselves.
+	 */
+	ts->tv_sec -= utc_offset();
 	nsec = (uint64_t)ts->tv_sec * 1000000000 + ts->tv_nsec;
 
 	mtx_lock(&sc->mtx);