drm/tve200: Check for IS_ERR instead of NULL in probe

devm_ioremap_resource() returns error pointer, it never returns NULL on
error.

Fixes: 179c02fe ("drm/tve200: Add new driver for TVE200")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170925102520.a7spymwqqbsczzz2@mwanda

drivers/gpu/drm/tve200/tve200_drv.c

@@ -225,7 +225,7 @@ static int tve200_probe(struct platform_device *pdev)
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	priv->regs = devm_ioremap_resource(dev, res);
-	if (!priv->regs) {
+	if (IS_ERR(priv->regs)) {
 		dev_err(dev, "%s failed mmio\n", __func__);
 		ret = -EINVAL;
 		goto clk_disable;