MPRIS: Set CanControl to true

In a refactor, we had accidentally changed the "CanControl" MPRIS
property to be false instead of true. This CL changes it back.

Bug: 1056629
Change-Id: Ie072f735bf10510f2c231d7d1f33d13f95101c80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2078974
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745530}