Change HSE for blupill,can only be XTAL

    The BLUEPILL board does have XTAL soldered, cannot be used with an external oscillator

Author: LordGuilly

targets/TARGET_STM/TARGET_STM32F1/TARGET_BLUEPILL_F103C8/device/system_clock.c

@@ -45,7 +45,7 @@
 
 
 /* Select the clock sources (other than HSI) to start with (0=OFF, 1=ON) */
-#define USE_PLL_HSE_EXTC (1) /* Use external clock */
+#define USE_PLL_HSE_EXTC (0) /* Use external clock */
 #define USE_PLL_HSE_XTAL (1) /* Use external xtal */