Do not seek when switching to background playback

Seeking during setting surface causes audible sound repetition. The seek
is not necessary if switching to background playback. Therefore the
sound issue can be avoided in such a case.

Bug: 35831966
Test: background playback

Change-Id: I0eecd7206bedb3b56b837bafe1a63f9a3f8c3703
1 file changed