Disable watchdog timer when the firmware boots

If it gets this far, the firmware is at least sort of running, so the
watchdog has served its purpose of resetting to the bootloader if
there's invalid firmware flashed to the device.

hal/m258ke/board.c

@@ -68,6 +68,9 @@ void Board_Init(void)
 
 	// Start the timer, prescaler = 48, so 1 MHz
 	TIMER0->CTL = TIMER_CTL_CNTEN_Msk | (3UL << TIMER_CTL_OPMODE_Pos) | 47;
+
+	// Disable WDT now; the main firmware is booted.
+	WDT->CTL = (6 << WDT_CTL_TOUTSEL_Pos);
 }
 
 /** Determines if a brownout was detected at startup