lavfi: name anonymous structs

libavfilter/buffersink.c

libavfilter/buffersrc.c

libavfilter/fifo.c

libavfilter/setpts.c

libavfilter/settb.c

libavfilter/vf_aspect.c

libavfilter/vf_blackframe.c

libavfilter/vf_boxblur.c

libavfilter/vf_crop.c

libavfilter/vf_cropdetect.c

libavfilter/vf_delogo.c

libavfilter/vf_drawbox.c

libavfilter/vf_drawtext.c

libavfilter/vf_fade.c

libavfilter/vf_fieldorder.c

libavfilter/vf_format.c

libavfilter/vf_hflip.c

libavfilter/vf_hqdn3d.h

libavfilter/vf_interlace.c

libavfilter/vf_libopencv.c