i2c: muxes: Fix return value check in mule_i2c_mux_probe()

If dev_get_regmap() fails, it returns NULL pointer not ERR_PTR(),
replace IS_ERR() with NULL pointer check, and return -ENODEV.

Fixes: d0f8e97 ("i2c: muxes: add support for tsd,mule-i2c multiplexer")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

drivers/i2c/muxes/i2c-mux-mule.c

@@ -66,8 +66,8 @@ static int mule_i2c_mux_probe(struct platform_device *pdev)
 	priv = i2c_mux_priv(muxc);
 
 	priv->regmap = dev_get_regmap(mux_dev->parent, NULL);
-	if (IS_ERR(priv->regmap))
-		return dev_err_probe(mux_dev, PTR_ERR(priv->regmap),
+	if (!priv->regmap)
+		return dev_err_probe(mux_dev, -ENODEV,
 				     "No parent i2c register map\n");
 
 	platform_set_drvdata(pdev, muxc);