Modify vp9_setup_interp_filters function

Took vp9_setup_scale_factors_for_frame() out from
vp9_setup_interp_filters(), so that it is only called once per
frame instead of per macroblock. Decoder tests showed a 1.5%
performance gain.

Change-Id: I770cb09eb2140ab85132f82aed388ac0bdd3a0aa
3 files changed