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: 3bdffa8ffb45 ("Input: Add N64 controller driver")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Wei Yongjun <[e-mail]>
Reviewed-by: Lauri Kasanen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/joystick/n64joy.c

···
 	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;
 	}