Fix initial delay bug on Teensy-LC

https://forum.pjrc.com/threads/28325-Teensy-LC-and-delay

teensy3/mk20dx128.c

@@ -718,6 +718,7 @@ void ResetHandler(void)
 
 	// initialize the SysTick counter
 	SYST_RVR = (F_CPU / 1000) - 1;
+	SYST_CVR = 0;
 	SYST_CSR = SYST_CSR_CLKSOURCE | SYST_CSR_TICKINT | SYST_CSR_ENABLE;
 	SCB_SHPR3 = 0x20200000;  // Systick = priority 32