stm32f1: maple LED is on A5.

Fix incorrect RCC port.  Only applies to "maple" not to maple mini.

Fixes github issue #117

Author: karlp

examples/stm32/f1/stm32-maple/miniblink/miniblink.c

@@ -26,7 +26,7 @@ static void gpio_setup(void)
 	/* Manually: */
 	// RCC_APB2ENR |= RCC_APB2ENR_IOPCEN;
 	/* Using API functions: */
-	rcc_periph_clock_enable(RCC_GPIOC);
+	rcc_periph_clock_enable(RCC_GPIOA);
 
 	/* Set GPIO5 (in GPIO port A) to 'output push-pull'. */
 	/* Manually: */