serial: imx: drop if that always evaluates to true

The check sts & USR1_DTRD was just evaluated to true two lines above.
So this change doesn't have any effect on the semantic of the driver.

Fixes: 27e1650 ("serial: imx: implement DSR irq handling for DTE mode")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -781,8 +781,7 @@ static irqreturn_t imx_int(int irq, void *dev_id)
 	if (sts & USR1_DTRD) {
 		unsigned long flags;
 
-		if (sts & USR1_DTRD)
-			writel(USR1_DTRD, sport->port.membase + USR1);
+		writel(USR1_DTRD, sport->port.membase + USR1);
 
 		spin_lock_irqsave(&sport->port.lock, flags);
 		imx_mctrl_check(sport);