lavc/mediacodec: rescale pts before decoding for both hw and sw buffers

Replicates the logic used in the wrap_hw_buffer path to wrap_sw_buffer
as well.

Fixes decoding issues observed on AMLogic devices with
OMX.amlogic.mpeg2.decoder.awesome, where the decoder would spit out a
constant stream of "mPtsRecoveryCount" errors and decoded frames were
returned in the incorrect order.

Signed-off-by: Matthieu Bouron <matthieu.bouron@gmail.com>