Fix typo in samd51 clock init

Author: rlcamp

cores/arduino/startup.c

@@ -63,7 +63,7 @@ void SystemInit( void )
    * 1) Enable XOSC32K clock (External on-board 32.768Hz oscillator)
    */
 
-  OSC32KCTRL->XOSC32K.reg = OSC32KCTRL_XOSC32K_ENABLE | OSC32KCTRL_XOSC32K_EN32K | OSC32KCTRL_XOSC32K_EN32K | OSC32KCTRL_XOSC32K_CGM_XT | OSC32KCTRL_XOSC32K_XTALEN;
+  OSC32KCTRL->XOSC32K.reg = OSC32KCTRL_XOSC32K_ENABLE | OSC32KCTRL_XOSC32K_EN1K | OSC32KCTRL_XOSC32K_EN32K | OSC32KCTRL_XOSC32K_CGM_XT | OSC32KCTRL_XOSC32K_XTALEN;
 
   while( (OSC32KCTRL->STATUS.reg & OSC32KCTRL_STATUS_XOSC32KRDY) == 0 ){
     /* Wait for oscillator to be ready */