[opus] error compiling when FIXED_POINT and DISABLE_FLOAT_API are defined

[Pedro Becerra]

Hello,
is the following a valid build option?
     ./configure CFLAGS="-g -O2 -DDISABLE_FLOAT_API" \
         --enable-assertions --enable-fixed-point

src/opus_multistream_encoder.c does not compile with that configuration.
--
Pedro Becerra