befs: fix build on parisc

fs/befs/super.c:85: error: 'PAGE_SIZE' undeclared

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>