codec2: Fix issues in Gapless playback C2SoftMP3

While the decoder delay samples are removed from output, adjust timestamp
and buffer size informations accordingly

Bug: 74770949
Test: setprop debug.stagefright.ccodec true
Test: stagefright -ao -N c2.google.mp3.decoder /sdcard/clips/bbb.mp3

Change-Id: Iac2a9eb119762f9ef45a53c1ff53ddd46adcff89