Revert "Revert "stm32f4: fix serial output""

Due to a misunderstanding, in 698a12b we reverted changes that we in
fact wanted to keep.  So lets fix that mistake and bring the code back
to how it should have been.

This reverts commit 698a12bef9.

Signed-off-by: Tom Rini <trini@konsulko.com>

drivers/serial/serial_stm32.c

@@ -128,6 +128,9 @@ static void stm32_serial_putc(const char c)
 	struct stm32_serial *usart =
 		(struct stm32_serial *)usart_base[USART_PORT];
 
+	if (c == '\n')
+		stm32_serial_putc('\r');
+
 	while ((readl(&usart->sr) & USART_SR_FLAG_TXE) == 0)
 		;
 	writel(c, &usart->dr);