lavf/davs2.c: rename as avs2dec.c for better understanding

Signed-off-by: hwren <hwrenx@126.com>

libavformat/Makefile

@@ -123,7 +123,7 @@ OBJS-$(CONFIG_AVI_MUXER)                 += avienc.o mpegtsenc.o avlanguage.o ra
 OBJS-$(CONFIG_AVM2_MUXER)                += swfenc.o swf.o
 OBJS-$(CONFIG_AVR_DEMUXER)               += avr.o pcm.o
 OBJS-$(CONFIG_AVS_DEMUXER)               += avs.o voc_packet.o vocdec.o voc.o
-OBJS-$(CONFIG_AVS2_DEMUXER)              += davs2.o rawdec.o
+OBJS-$(CONFIG_AVS2_DEMUXER)              += avs2dec.o rawdec.o
 OBJS-$(CONFIG_AVS2_MUXER)                += rawenc.o
 OBJS-$(CONFIG_AVS3_DEMUXER)              += avs3dec.o rawdec.o
 OBJS-$(CONFIG_BETHSOFTVID_DEMUXER)       += bethsoftvid.o