Input: n64joy - fix return value check in n64joy_probe()

In case of error, the function devm_platform_ioremap_resource()
returns ERR_PTR() and never returns NULL. The NULL test in the
return value check should be replaced with IS_ERR().

Fixes: 3bdffa8f ("Input: Add N64 controller driver")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: NLauri Kasanen <cand@gmx.com>
Link: https://lore.kernel.org/r/20210308122856.2177071-1-weiyongjun1@huawei.comSigned-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/joystick/n64joy.c

@@ -252,8 +252,8 @@ static int __init n64joy_probe(struct platform_device *pdev)
 	mutex_init(&priv->n64joy_mutex);
 
 	priv->reg_base = devm_platform_ioremap_resource(pdev, 0);
-	if (!priv->reg_base) {
-		err = -EINVAL;
+	if (IS_ERR(priv->reg_base)) {
+		err = PTR_ERR(priv->reg_base);
 		goto fail;
 	}