Inline vp9_quantize() in xform_quant().

Cycle times:
4x4:    151 to  131 cycles (15% faster)
8x8:    334 to  306 cycles (9% faster)
16x16: 1401 to 1368 cycles (2.5% faster)
32x32: 7403 to 7367 cycles (0.5% faster)

Total encode time of first 50 frames of bus @ 1500kbps (speed 0)
goes from 1min39.2 to 1min38.6, i.e. a 0.67% overall speedup.

Change-Id: I799a49460e5e3fcab01725564dd49c629bfe935f