The 8 bits offset (nal unit type) should not be added, as the spec says:

"This bit offset is the offset within the RBSP data for the slice, relative
to the starting position of the slice_header() in the RBSP"

This fixes DXVA2 support for intel GPU.

Patch by Rafaël Carré (funman _AT_ videolan _DOT_ org).

Originally committed as revision 25538 to svn://svn.ffmpeg.org/ffmpeg/trunk