phy: Sparx5 Eth SerDes: Fix return value check in sparx5_serdes_probe()

In case of error, the function devm_ioremap() returns NULL
pointer not ERR_PTR(). The IS_ERR() test in the return value
check should be replaced with NULL test.

Fixes: 2ff8a1eeb5aa ("phy: Add Sparx5 ethernet serdes PHY driver")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Yang Yingliang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/phy/microchip/sparx5_serdes.c

···
 		return -EINVAL;
 	}
 	iomem = devm_ioremap(priv->dev, iores->start, resource_size(iores));
-	if (IS_ERR(iomem)) {
+	if (!iomem) {
 		dev_err(priv->dev, "Unable to get serdes registers: %s\n",
 			iores->name);
-		return PTR_ERR(iomem);
+		return -ENOMEM;
 	}
 	for (idx = 0; idx < ARRAY_SIZE(sparx5_serdes_iomap); idx++) {
 		struct sparx5_serdes_io_resource *iomap = &sparx5_serdes_iomap[idx];