Fix invalid out-of-bounds store in MacroAssembler::Allocate.

This fixes an out-of-bounds store in inlined allocations when double
alignment and pretenuring into old-data-space have been requested.

R=hpayer@chromium.org, jkummerow@chromium.org, plind44@gmail.com
BUG=chromium:263515

Review URL: https://codereview.chromium.org/23242006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16224 ce2b1a6d-e550-0410-aec6-3dcde31c8c00