touchscreen: Fix seeking to end of track in WPS
Seeking to the very end of the track with the touchscreen caused
rapid skipping through the playlist because each touch event
generates a separate seek operation, kind of like rapidly pressing
a physical button. Fix this bug by executing the seek operation
only for the release event.
Change-Id: Ic1080065a68e7cc2ba98e2f27293c954f2ec8fb2