drivers: serial: stm32: Fix possible issue with mixed enum

When building with LLVM we get the following error:

uart_stm32.c:272:9: error: implicit conversion from enumeration type
'enum uart_config_parity' to different enumeration type
'enum uart_config_flow_control' [-Werror,-Wenum-conversion]
        return UART_CFG_PARITY_NONE;
        ~~~~~~ ^~~~~~~~~~~~~~~~~~~~

We shouldn't be mixing parity and flow control enum's.  Use
UART_CFG_FLOW_CTRL_NONE instead or UART_CFG_PARITY_NONE.

Signed-off-by: Kumar Gala <[email protected]>

Author: galak

drivers/serial/uart_stm32.c

@@ -261,15 +261,15 @@ static inline u32_t uart_stm32_cfg2ll_hwctrl(enum uart_config_flow_control fc)
  *         LL hardware flow control define.
  * @note   Supports only LL_USART_HWCONTROL_RTS_CTS.
  * @param  fc: LL hardware frlow control definition.
- * @retval UART_CFG_FLOW_CTRL_RTS_CTS, or UART_CFG_PARITY_NONE.
+ * @retval UART_CFG_FLOW_CTRL_RTS_CTS, or UART_CFG_FLOW_CTRL_NONE.
  */
 static inline enum uart_config_flow_control uart_stm32_ll2cfg_hwctrl(u32_t fc)
 {
 	if (fc == LL_USART_HWCONTROL_RTS_CTS) {
 		return UART_CFG_FLOW_CTRL_RTS_CTS;
 	}
 
-	return UART_CFG_PARITY_NONE;
+	return UART_CFG_FLOW_CTRL_NONE;
 }
 
 static int uart_stm32_configure(struct device *dev,