MAINTAINERS: Add missing section for alienware-wmi driver

This driver is maintained by Dell, but it was missing in MAINTAINERS.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Link: https://lore.kernel.org/r/20210401162206.26901-3-mario.limonciello@dell.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>