avcodec/mips/aaccoder_mips: Sync with generic aaccoder file.

Code in aaccoder_mips.c was not synced with changes in aaccoder.c for
some time.

That was cause for some fate-aac tests failing.

This patch fixes the problems.

Optimizations disabled in 933309a6 are enabled again.
Signed-off-by: Nedeljko Babic <nedeljko.babic@imgtec.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>