serial: imx: fix throttle/unthrottle callbacks for hardware assisted flow control

when the 'CTSC' bit is negated. 'CTS' has no function when 'CTSC' is asserted.
0: The CTS pin is high (inactive)
1: The CTS pin is low (active)

For throttle, it needs to clear 'CTS' and 'CTSC' bits.
For unthrottle, it needs to enable 'CTS' and 'CTSC' bits.

The patch just fix the issue.
Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -817,11 +817,9 @@ static void imx_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	struct imx_port *sport = (struct imx_port *)port;
 	unsigned long temp;
 
-	temp = readl(sport->port.membase + UCR2) & ~UCR2_CTS;
-
+	temp = readl(sport->port.membase + UCR2) & ~(UCR2_CTS | UCR2_CTSC);
 	if (mctrl & TIOCM_RTS)
-		if (!sport->dma_is_enabled)
-			temp |= UCR2_CTS;
+		temp |= UCR2_CTS | UCR2_CTSC;
 
 	writel(temp, sport->port.membase + UCR2);