staging/lustre: Get rid of CFS_PAGE_MASK

CFS_PAGE_MASK is the same as PAGE_MASK, so get rid of it.

We are replacing it with PAGE_MASK instead of PAGE_CACHE_MASK
because PAGE_CACHE_* stuff is apparently going away.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>