platform/x86: intel/rst: 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 intel/rst driver.

Fixes: 163a68a ("platform/x86: intel/rst: 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/2051525.PYKUYFuaPT@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/intel/rst.c

@@ -102,9 +102,13 @@ static struct device_attribute irst_timeout_attr = {
 
 static int irst_probe(struct platform_device *pdev)
 {
-	struct acpi_device *acpi = ACPI_COMPANION(&pdev->dev);
+	struct acpi_device *acpi;
 	int error;
 
+	acpi = ACPI_COMPANION(&pdev->dev);
+	if (!acpi)
+		return -ENODEV;
+
 	error = device_create_file(&acpi->dev, &irst_timeout_attr);
 	if (unlikely(error))
 		return error;