serial: imx: initialize the local variable

The slave_config is not initialized, so some of its fields may
be set with random data which may causes the failure in the following
dmaengine_prep_slave_sg().

This patch fixes this issue.
Signed-off-by: Huang Shijie <b32955@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -979,7 +979,7 @@ static void imx_uart_dma_exit(struct imx_port *sport)
 
 static int imx_uart_dma_init(struct imx_port *sport)
 {
-	struct dma_slave_config slave_config;
+	struct dma_slave_config slave_config = {};
 	struct device *dev = sport->port.dev;
 	int ret;