When switching surface, do not set mSeekNotificationSent as true,

because there could be a previous uncompleted seeking which needs
to send back MEDIA_SEEK_COMPLETE message. If we set mSeekNotificationSent
as true here, then mediaplayer.cpp will be waiting for message
MEDIA_SEEK_COMPLETE. The getCurrentPosition() will always return
the seek time before MEDIA_SEEK_COMPLETE being received by mediaplayer.cpp.
Fix for bug 5181272.

Change-Id: I290aff29b6d9ec8db67c66abbe1f352a43f57073