vpx_highbd_d153_predictor_4x4_sse2: reduce load size
vpx_highbd_d153_predictor_4x4_sse2: reduce load size

this avoids reading 4 pixels into another block, which may be operated
on by a different thread. quiets a tsan warning.

Change-Id: Id27ad9d61819b0e5de0230647b4b510f7c265a71

webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx