Linux: Fix an error from r249340. RAMFS_MAGIC != HUGETLBFS_MAGIC

Review URL: https://codereview.chromium.org/173363004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252449 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252449