drm: sti: tvout: fix return value check in sti_tvout_probe()

In case of error, the function devm_ioremap_nocache() returns NULL
pointer not ERR_PTR(). The IS_ERR() test in the return value check
should be replaced with NULL test.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>

drivers/gpu/drm/sti/sti_tvout.c

@@ -591,8 +591,8 @@ static int sti_tvout_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	}
 	tvout->regs = devm_ioremap_nocache(dev, res->start, resource_size(res));
-	if (IS_ERR(tvout->regs))
-		return PTR_ERR(tvout->regs);
+	if (!tvout->regs)
+		return -ENOMEM;
 
 	/* get reset resources */
 	tvout->reset = devm_reset_control_get(dev, "tvout");