mpeg2enc: Fix top_field_first
mpeg2enc: Fix top_field_first

Signed-off-by: Xiang, Haihao <8d677183e5993577d4fa73a419b76987913292d6@intel.com>

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