mm: thp: avoid false positive VM_BUG_ON_PAGE in page_move_anon_rmap()

If page_move_anon_rmap() is refiling a pmd-splitted THP mapped in a tail
page from a pte, the "address" must be THP aligned in order for the
page->index bugcheck to pass in the CONFIG_DEBUG_VM=y builds.

Link: http://lkml.kernel.org/r/1464253620-106404-1-git-send-email-kirill.shutemov@linux.intel.com
Fixes: 6d0a07ed

 ("mm: thp: calculate the mapcount correctly for THP pages during WP faults")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>        [4.5]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>