avcodec/adpcm: also squelch 'mismatch in coded sample count' warning for AV_CODEC_ID_ADPCM_EA_R1

AV_CODEC_ID_ADPCM_EA_R1/R2/R3 all use an internal offset. For some
samples there is padding between the offset table and ADPCM data.

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>