move format.c definition to correct modules.am-file

modules/audio_filter/Modules.am

 SUBDIRS = channel_mixer converter resampler spatializer
 SOURCES_equalizer = equalizer.c equalizer_presets.h
 SOURCES_normvol = normvol.c
-SOURCES_audio_format = converter/format.c
 SOURCES_param_eq = param_eq.c
 SOURCES_scaletempo = scaletempo.c
 SOURCES_chorus_flanger = chorus_flanger.c

modules/audio_filter/converter/Modules.am

@@ -6,6 +6,7 @@ SOURCES_a52tofloat32 = a52tofloat32.c
 SOURCES_dtstospdif = dtstospdif.c
 SOURCES_dtstofloat32 = dtstofloat32.c
 SOURCES_mpgatofixed32 = mpgatofixed32.c
+SOURCES_audio_format = format.c
 
 libvlc_LTLIBRARIES += \
 	libconverter_fixed_plugin.la \