Test results:

before:
  fate-suite/vc1/SA10091.vc1: 1062 decicycles in ff_vc1_mc_4mv_chroma's get mv, 4089 runs, 7 skips
  fate-suite/vc1/SA10143.vc1: 1112 decicycles in ff_vc1_mc_4mv_luma's get mv, 4096 runs, 0 skips
  fate-suite/vc1/SA20021.vc1: 991 decicycles in ff_vc1_mc_4mv_chroma get mv, 8192 runs, 0 skips

after:
  fate-suite/vc1/SA10091.vc1: 940 decicycles in ff_vc1_mc_4mv_chroma's get mv, 4096 runs, 0 skips
  fate-suite/vc1/SA10143.vc1: 786 decicycles in ff_vc1_mc_4mv_luma's get mv, 4096 runs, 0 skips
  fate-suite/vc1/SA20021.vc1: 876 decicycles in ff_vc1_mc_4mv_chroma get mv, 8189 runs, 3 skips
Signed-off-by: Zeng Zhaoxiu <zhaoxiu.zeng@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>