eeepc-wmi: Use acpi_dev_found()

Use shiny new acpi_dev_found() and remove all the boilerplate
to search for a particular ACPI device. No functional change.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>