This fixes decoding, broken since 7e35037.
This is similar to what was done for the normal mp3 decoder in
f4a86bc9.
Signed-off-by: Martin Storsjö <martin@martin.st>
The CONFIG_ name-space is set by configure, so its better to use a
different prefix here.
This also unifies the encoder & decoder define that is used
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>