platform/x86: mlx-platform: Fix an ERR_PTR vs NULL issue

devm_ioport_map() returns NULL on error but we accidentally check for
error pointers instead.

Fixes: c6acad68 ("platform/mellanox: mlxreg-hotplug: Modify to use a regmap interface")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Vadim Pasternak <vadimp@melanox.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

drivers/platform/x86/mlx-platform.c

@@ -522,8 +522,8 @@ static int __init mlxplat_init(void)
 
 	mlxplat_mlxcpld_regmap_ctx.base = devm_ioport_map(&mlxplat_dev->dev,
 			       mlxplat_lpc_resources[1].start, 1);
-	if (IS_ERR(mlxplat_mlxcpld_regmap_ctx.base)) {
-		err = PTR_ERR(mlxplat_mlxcpld_regmap_ctx.base);
+	if (!mlxplat_mlxcpld_regmap_ctx.base) {
+		err = -ENOMEM;
 		goto fail_platform_mux_register;
 	}