pch_uart: check kzalloc result in dma_handle_tx()

Reported by coccinelle:

drivers/tty/serial/pch_uart.c:979:1-14: alloc with no test, possible model on line 994
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/pch_uart.c

@@ -979,6 +979,10 @@ static unsigned int dma_handle_tx(struct eg20t_port *priv)
 	priv->tx_dma_use = 1;
 
 	priv->sg_tx_p = kzalloc(sizeof(struct scatterlist)*num, GFP_ATOMIC);
+	if (!priv->sg_tx_p) {
+		dev_err(priv->port.dev, "%s:kzalloc Failed\n", __func__);
+		return 0;
+	}
 
 	sg_init_table(priv->sg_tx_p, num); /* Initialize SG table */
 	sg = priv->sg_tx_p;