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: Id08af4200fea9e1b896fc40157b8651c2c7e80f2