riff: support 0xa100 TwoCC

fixes decoding of file "4790b7f1c44f98e35f3b806468fa615f5930a5b3.wav" from ticket #1856
(0xa100 = Comverse Infosys Ltd. G723 1)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/riff.c

@@ -373,6 +373,7 @@ const AVCodecTag ff_codec_wav_tags[] = {
     { AV_CODEC_ID_PCM_MULAW,       0x6c75 },
     { AV_CODEC_ID_AAC,             0x706d },
     { AV_CODEC_ID_AAC,             0x4143 },
+    { AV_CODEC_ID_G723_1,          0xA100 },
     { AV_CODEC_ID_SPEEX,           0xA109 },
     { AV_CODEC_ID_FLAC,            0xF1AC },
     { AV_CODEC_ID_ADPCM_SWF,       ('S'<<8)+'F' },