serial: imx: Fix issue in software flow control

After send out x_char in UART driver, x_char needs to be cleared
by UART driver itself, otherwise data in TXFIFO can no longer be
sent out.
Also tx counter needs to be increased to keep track of correct
number of transmitted data.
Signed-off-by: NJiada Wang <jiada_wang@mentor.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -471,6 +471,8 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
 	if (sport->port.x_char) {
 		/* Send next char */
 		writel(sport->port.x_char, sport->port.membase + URTX0);
+		sport->port.icount.tx++;
+		sport->port.x_char = 0;
 		return;
 	}