Values of MODE_UPDATE_PROB and VP9_COEF_UPDATE_PROB are equal, so replacing
them with one constant. Inlining appropriate arguments for functions:
  vp9_cond_prob_diff_update (encoder)
  vp9_diff_update_prob (decoder)

Change-Id: I1255a1cb477743b799b3bfbbcd8de6b32b067338