serial8250-em: clk_get() IS_ERR() error handling fix

Update the 8250_em driver to correctly handle the case
where no clock is associated with the device.

The return value of clk_get() needs to be checked with
IS_ERR() to avoid NULL pointer referencing.
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_em.c

@@ -110,8 +110,9 @@ static int __devinit serial8250_em_probe(struct platform_device *pdev)
 	}
 
 	priv->sclk = clk_get(&pdev->dev, "sclk");
-	if (!priv->sclk) {
+	if (IS_ERR(priv->sclk)) {
 		dev_err(&pdev->dev, "unable to get clock\n");
+		ret = PTR_ERR(priv->sclk);
 		goto err1;
 	}