Fix DBus signals in Mprisremote
Summary: This seems to fix the issue I mentioned on Telegram/Mail
Test Plan:
Before: Use Mprisremote plugin with App. View did not update when e.g. next is pressed.
Now: View correctly represents the DBus data
Reviewers: KDE Connect
Subscribers: KDE Connect
Tags: KDE Connect
Differential Revision: https://phabricator.kde.org/D12528