API: h264 decode: clarify slice_data_bit_offset field.
API: h264 decode: clarify slice_data_bit_offset field.

slice_data_bit_offset represents a bit offset from the NAL Header Unit
byte to the begining of the slice_data(), thus including any emulation
prevention bytes. Baiscally, this represents the number of bits parsed
for slice_header().

Signed-off-by: Gwenole Beauchesne <729713629d9640cc095f1c77c692e1881f8093c4@intel.com>

Distrotech/libva,gbeauchesne/libva,chenxianqin/vaapi-libva,pma1/libva,gbeauchesne/libva,01org/libva-cros,01org/iotg-lin-gfx-libva,pma1/libva,chenxianqin/vaapi-libva,pma1/libva,01org/iotg-lin-gfx-libva,gbeauchesne/libva,01org/libva-cros,zzhhui/libva,chenxianqin/vaapi-libva,zzhhui/libva,zzhhui/libva,Distrotech/libva,01org/iotg-lin-gfx-libva,Distrotech/libva,01org/libva-cros