Fix for failing asserts in HBoundsCheck code generation on x64: use proper cmp operation width instead of asserting that Integer32 values should be zero extended. Similar to chromium:345820.

BUG=349465
LOG=N
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/188703002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19694 ce2b1a6d-e550-0410-aec6-3dcde31c8c00