avfilter: don't anonymously typedef structs

libavfilter/aeval.c

libavfilter/af_afade.c

libavfilter/af_amerge.c

libavfilter/af_apad.c

libavfilter/af_aresample.c

libavfilter/af_asetnsamples.c

libavfilter/af_asetrate.c

libavfilter/af_astats.c

libavfilter/af_atempo.c

libavfilter/af_earwax.c

libavfilter/af_firequalizer.c

libavfilter/af_hdcd.c

libavfilter/af_volumedetect.c

libavfilter/asrc_anoisesrc.c

libavfilter/asrc_anullsrc.c

libavfilter/asrc_flite.c

libavfilter/asrc_sine.c

libavfilter/avf_concat.c

libavfilter/avf_showcqt.h

libavfilter/avf_showspectrum.c