avcodec: Add little-endian G726 decoder

Fixes part of Ticket1955
suggested by Roman.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/avcodec.h

@@ -377,6 +377,7 @@ enum AVCodecID {
     AV_CODEC_ID_ADPCM_IMA_OKI = MKBETAG('O','K','I',' '),
     AV_CODEC_ID_ADPCM_DTK  = MKBETAG('D','T','K',' '),
     AV_CODEC_ID_ADPCM_IMA_RAD = MKBETAG('R','A','D',' '),
+    AV_CODEC_ID_ADPCM_G726LE = MKBETAG('6','2','7','G'),
 
     /* AMR */
     AV_CODEC_ID_AMR_NB = 0x12000,