configure: fix libavfilter pkgconfig description

Signed-off-by: NPaul B Mahol <onemda@gmail.com>

configure

@@ -4596,7 +4596,7 @@ pkgconfig_generate libavutil "FFmpeg utility library" "$LIBAVUTIL_VERSION" "$LIB
 pkgconfig_generate libavcodec "FFmpeg codec library" "$LIBAVCODEC_VERSION" "$extralibs" "libavutil${build_suffix} = $LIBAVUTIL_VERSION"
 pkgconfig_generate libavformat "FFmpeg container format library" "$LIBAVFORMAT_VERSION" "$extralibs" "libavcodec${build_suffix} = $LIBAVCODEC_VERSION"
 pkgconfig_generate libavdevice "FFmpeg device handling library" "$LIBAVDEVICE_VERSION" "$extralibs" "$libavdevice_pc_deps"
-pkgconfig_generate libavfilter "FFmpeg video filtering library" "$LIBAVFILTER_VERSION" "$extralibs" "$libavfilter_pc_deps"
+pkgconfig_generate libavfilter "FFmpeg audio/video filtering library" "$LIBAVFILTER_VERSION" "$extralibs" "$libavfilter_pc_deps"
 pkgconfig_generate libpostproc "FFmpeg postprocessing library" "$LIBPOSTPROC_VERSION" "" "libavutil${build_suffix} = $LIBAVUTIL_VERSION"
 pkgconfig_generate libavresample "Libav audio resampling library" "$LIBAVRESAMPLE_VERSION" "$extralibs" "libavutil${build_suffix} = $LIBAVUTIL_VERSION"
 pkgconfig_generate libswscale "FFmpeg image rescaling library" "$LIBSWSCALE_VERSION" "$LIBM" "libavutil${build_suffix} = $LIBAVUTIL_VERSION"