hp-wmi: Switch driver to dev_pm_ops

Gets rid of the following warning:

Platform driver 'hp-wmi' needs updating - please use dev_pm_ops

I tested that the resume handler still works on my HP 2510p notebook.

[rjw: Fixed up the definition of hp_wmi_pm_ops.]

Signed-off-by: Frans Pop <elendil@planet.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>