row_neon64 fix for warning on ios where int width doesnt match %2 size which is…

row_neon64 fix for warning on ios where int width doesnt match %2 size which is 64 bit by default.  change size to explicitely 32 bit with %w2.
BUG=437
TESTED=try bots
R=bcornell@google.com

Review URL: https://webrtc-codereview.appspot.com/47119004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1399 16f28f9a-4ce2-e073-06de-1de4eb20be90