Rename asfdec-o.c to asfdec_o.c

Most files use _ instead of - as spacer, so this is more consistent
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/Makefile

@@ -84,7 +84,7 @@ OBJS-$(CONFIG_APNG_MUXER)                += apngenc.o
 OBJS-$(CONFIG_AQTITLE_DEMUXER)           += aqtitledec.o subtitles.o
 OBJS-$(CONFIG_ASF_DEMUXER)               += asfdec_f.o asf.o asfcrypt.o \
                                             avlanguage.o
-OBJS-$(CONFIG_ASF_O_DEMUXER)             += asfdec-o.o asf.o asfcrypt.o \
+OBJS-$(CONFIG_ASF_O_DEMUXER)             += asfdec_o.o asf.o asfcrypt.o \
                                             avlanguage.o
 OBJS-$(CONFIG_ASF_MUXER)                 += asfenc.o asf.o
 OBJS-$(CONFIG_ASS_DEMUXER)               += assdec.o subtitles.o