update deprecated function ( avcodec_alloc_frame, get_buffer, avcodec_default_get_buffer )

avcodec_alloc_frame -> av_frame_alloc
avcodec_default_get_buffer -> avcodec_default_get_buffer2
get_buffer -> get_buffer2

... and clean space at end of line.

need also to update:
- avcodec_default_release_buffer
- release_buffer