fwget: pci: mediatek: correct package name

The port is called wifi-firmware-mt76-kmod not "mediatek" in the
moddle.

Reported by: Lars Tunkrans (drsnx60 gmail.com)
MFC after: 3 days
Reviewed by: emaste, jrm, imp
Differential Revision: https://reviews.freebsd.org/D53067