fix USB read received character

main.c

@@ -470,7 +470,7 @@ int main(void)
 		while (cdcacm_received) { // data received over USB
 			action = true; // action has been performed
 			led_toggle(); // toggle LED
-			c = usart_getchar(); // store receive character
+			c = cdcacm_getchar(); // store receive character
 			char_flag = true; // notify character has been received
 		}
 		while (char_flag) { // user data received