platform/x86: system76: Check ACPI_COMPANION() against NULL

Every platform driver can be forced to match a device that doesn't match
its list of device IDs because of device_match_driver_override(), so
platform drivers that rely on the existence of a device's ACPI companion
object need to verify its presence.

Accordingly, add a requisite ACPI_COMPANION() check against NULL to the
platform/x86 system76 driver.

Fixes: 80b8f68 ("platform/x86: system76: Convert ACPI driver to a platform one")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/2072699.usQuhbGJ8B@rafael.j.wysocki
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: rafaeljw

drivers/platform/x86/system76_acpi.c

@@ -674,10 +674,14 @@ static void system76_notify(acpi_handle handle, u32 event, void *context)
 // Probe a System76 platform device
 static int system76_probe(struct platform_device *pdev)
 {
-	struct acpi_device *acpi_dev = ACPI_COMPANION(&pdev->dev);
+	struct acpi_device *acpi_dev;
 	struct system76_data *data;
 	int err;
 
+	acpi_dev = ACPI_COMPANION(&pdev->dev);
+	if (!acpi_dev)
+		return -ENODEV;
+
 	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;