Fix handling of Integer32 in HLoadNamedField and HStoreNamedField on x64.

The current implementation of Integer32 named loads and stores
is broken on x64.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/23548039

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16750 ce2b1a6d-e550-0410-aec6-3dcde31c8c00