serial: imx: Remove unused 'tty' variable

Commit 2e124b4a (TTY: switch tty_flip_buffer_push) introduced the following
build warning:

drivers/tty/serial/imx.c:519:21: warning: unused variable 'tty' [-Wunused-variable]

Remove the unused 'tty' variable.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -516,7 +516,6 @@ static irqreturn_t imx_rxint(int irq, void *dev_id)
 {
 	struct imx_port *sport = dev_id;
 	unsigned int rx, flg, ignored = 0;
-	struct tty_struct *tty = sport->port.state->port.tty;
 	struct tty_port *port = &sport->port.state->port;
 	unsigned long flags, temp;