ceph: fix page alignment corrections

 dd if=/dev/urandom of=/mnt/fs_depot/dd10 bs=500 seek=8388 count=1
 dd if=/mnt/fs_depot/dd10 of=/root/dd10out bs=500 skip=8388 count=1

Reported-by: Henry C Chang <henry.cy.chang@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>