libvpx

Fix decoder mismatch with ssse3 enabled

This patch fixed issue 661: "Decoder produces mismatched outputs
with ssse3 enabled and disabled." In sub-pixel filters, a pixel
value was multiplied by a filter coefficient, and the results
were added up. The order of adding up these multiplications had to
be arranged carefully to prevent incorrect overflowing.

Change-Id: Ia78663dfe74a2d46900f1c6fb07c21fac273892f