ceph: fix atomic64_t initialization on ia64

bdi_seq is an atomic_long_t but we're using ATOMIC_INIT, which causes
 build failures on ia64. This patch fixes it to use ATOMIC_LONG_INIT.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Sage Weil <sage@newdream.net>