[3.0] inhibit/dbus: fix service and path

Backport of !3316 (merged)

According to https://web.archive.org/web/20080828095706/https://people.freedesktop.org/~hughsient/temp/power-management-spec-0.2.html the correct service name does not include .Inhibit and the path includes /Inhibit.

This essentially reverts beec9e78

(cherry picked from commit 77a2d21b)