About 1% faster ff_ac3_bit_alloc_calc_psd on Intel Atom, overall speedup
not measurable though.
Should have a bigger effect on systems without cmov or with very slow cmov.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@21214 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b