Update quantize SSSE3 SIMD to cover 32x32 transform case also.

Encode time of bus (speed 0) 50 frames @ 1500kbps goes from 2min14.4 to
2min10.1, i.e. a 2.3% overall speed increase.

Change-Id: I3699580e74ec26c7d24e03681bc47ba25ee1ee87