frameworks/av: Fix for video playback failure in browser

- Issue: After camping the Signal to 3G network, open the browser
and go to www.youtube.com and play any video. Video playback is
failing after trying to load the video for few seconds. Browser is
coming back to video's list.

- Cause: At the beginning of playback, as there was a seek request
pending, seek is done before starting the AudioPlayer. After
AudioSource seeking, AudioPlayer start is called with OMX in PAUSED
state, causing assert check fail for OMX state.

- Fix: Call AudioSource start before calling AudioPlayer start, so that
OMX moves to EXECUTING state.

(Fix is ported from ICS I4e746bf0b5167d4998fd900bbce3966a2dc1273d)
CRs-Fixed: 395384

Change-Id: Id4f7e8658ba96b28533d11d34d4622ea6106615d