serial: stm32: fix pio transmit timeout

100µs was too short for low speed transmission
(9600bps)

Signed-off-by: Gerald Baeza <gerald.baeza@st.com>
Signed-off-by: Bich Hemon <bich.hemon@st.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -203,7 +203,7 @@ static void stm32_transmit_chars_pio(struct uart_port *port)
 	ret = readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr,
 						isr,
 						(isr & USART_SR_TXE),
-						10, 100);
+						10, 100000);
 
 	if (ret)
 		dev_err(port->dev, "tx empty not set\n");