drivers/generic/max98357a: Fix naming and ACPI path handling

The upstream kernel driver is not using the of-style naming for
sdmode-gpio so remove the maxim prefix, and remove the duplicate
entry for the sdmode-delay value as well.

Also fix the usage of the path variable, since the device path uses
a static variable it can't be assigned that early or it will be
overwritten by later calls.

This results in the following output for the _DSD when tested on
reef mainboard:

Name (_DSD, Package (0x02)
{
    ToUUID ("daffd814-6eba-4d8c-8a91-bc9bbf4aa301")
    Package (0x02)
    {
        Package (0x02)
        {
            "sdmode-gpio",
            Package (0x04)
            {
                \_SB.PCI0.HDAS.MAXM,
                Zero,
                Zero,
                Zero
            }
        },
        Package (0x02)
        {
            "sdmode-delay",
            Zero
        }
    }
})

Change-Id: Iab33182a5f64c89151966f5e79f4f7c30840c46f
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/15514
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/drivers/generic/max98357a/max98357a.c b/src/drivers/generic/max98357a/max98357a.c
index cbd7efd..0d522d4 100644
--- a/src/drivers/generic/max98357a/max98357a.c
+++ b/src/drivers/generic/max98357a/max98357a.c
@@ -31,9 +31,9 @@
 static void max98357a_fill_ssdt(struct device *dev)
 {
 	struct drivers_generic_max98357a_config *config = dev->chip_info;
-	const char *path = acpi_device_path(dev);
+	const char *path;
 
-	if (!dev->enabled || !path || !config)
+	if (!dev->enabled || !config)
 		return;
 
 	/* Device */
@@ -53,10 +53,8 @@
 	/* _DSD for devicetree properties */
 	acpi_dp_write_header();
 	/* This points to the first pin in the first gpio entry in _CRS */
-	acpi_dp_write_gpio("maxim,sdmode-gpio", path, 0, 0, 0);
-	/* This is the correctly formatted Device Property name */
-	acpi_dp_write_integer("maxim,sdmode-delay", config->sdmode_delay);
-	/* This is used by the chromium kernel but is not upstream */
+	path = acpi_device_path(dev);
+	acpi_dp_write_gpio("sdmode-gpio", path, 0, 0, 0);
 	acpi_dp_write_integer("sdmode-delay", config->sdmode_delay);
 	acpi_dp_write_footer();