libavcodec/qsvdec_h2645.c: switch to the new BSF API

This patch applies same changes as commit e3dfef8e of libav:
instead of the obsolete AVBitStreamFilterContext now the new AVBSFContext filter is used to
restore annex-B prefixes.

Based-on: e3dfef8e by Anton Khirnov
Push requested by maintainer
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>