ffmpeg: put the sizeof() second in av_malloc_array()

This is purely a cosmetic change
Suggested-by: Clément Bœsch <u@pkh.me>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/utils: ff_decode_frame_props: set pkt_size

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/utils: merge ff_decode_frame_props() and ff_init_buffer_info()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>