Use RCC_CFGR_SW helper function to set software clock

src/main.c

@@ -65,8 +65,7 @@ static void system_clock_init(void) {
   RCC->CFGR |= (FLASH_ACR_LATENCY_3_WAIT_STATES << FLASH_ACR_LATENCY_BIT);
 
   // Use PLL as system clock
-  RCC->CFGR &= ~(RCC_CFGR_SW_MASK << RCC_CFGR_SW_BIT);
-  RCC->CFGR |= (RCC_CFGR_SW_PLL << RCC_CFGR_SW_BIT);
+  RCC->CFGR |= RCC_CFGR_SW(RCC_CFGR_SW_PLL);
 
   // Wait indefinitely for PLL clock to be selected
   // TODO indicate error/timeout somehow?