vp9: fix compilation for g++ 6.2.x
vp9: fix compilation for g++ 6.2.x

Inline function called from test/dct16x16_test.cc wouldn't build due to:
  invalid operands of types ‘__gnu_cxx::__enable_if<true, double>::__type
  {aka double}’ and ‘int’ to binary ‘operator>>’
  return (abs(ref->row) >> 3) < COMPANDED_MVREF_THRESH &&

this converts the test to abs() < COMPANDED_MVREF_THRESH << 3 which
hides the promotion issue.

Regression from commit de993a847f8080d3128420c8ef8495642013bdb1

BUG=webm:1291

Change-Id: I73b5943d07d5b61b709d299114216a2371a8fd62

mwgoldsmith/vpx,mwgoldsmith/vpx,mwgoldsmith/vpx,mwgoldsmith/vpx,webmproject/libvpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,Topopiccione/libvpx,webmproject/libvpx,Topopiccione/libvpx,mwgoldsmith/vpx,Topopiccione/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,Topopiccione/libvpx,Topopiccione/libvpx