C2SoftOpusDec: fix pts gap after first output sample

for the first output frame, opus component after decoding will discard
few samples. This is dependent on mCodecDelay or mSeekPreRoll. As the
output samples are discarded, the output timestamp also needs to be
proportionately adjusted. This is addressed.

Bug: 139484367
Test: atest MctsMediaV2TestCases -- --module-arg \
  MctsMediaV2TestCases:instrumentation-arg:media-type-sel:=opus
Test: atest MctsMediaDecoderTestCases:DecoderTest
Test: atest VtsHalMediaC2V1_0TargetAudioDecTest
Flag: EXEMPT bugfix
Change-Id: Iad44d37a7d49c2e8795422b726c6806707ffd7d8