STM32F031K6 Missing UART_RX Pin Def

PA3 on the STM32F031K6 can function as a USART1_RX pin.

Author: ksitko

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F0/TARGET_NUCLEO_F031K6/PeripheralPins.c

@@ -109,6 +109,7 @@ const PinMap PinMap_UART_TX[] = {
 };
 
 const PinMap PinMap_UART_RX[] = {
+    {PA_3, UART_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_USART1)},
     {PA_10, UART_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_USART1)},
     {PA_15, UART_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_USART1)}, // STDIO RX
     {PB_7,  UART_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF0_USART1)},