libvpx

Fix high bit depth assembly function bugs

The high bit depth build failed while building for 32bit target.
The bugs were in vp9_highbd_subpel_variance.asm and
vp9_highbd_sad4d_sse2.asm functions. This patch fixed the bugs,
and made 32bit build work.

Change-Id: Idc8e5e1b7965bb70d4afba140c6583c5d9666b75