vfs_ceph: explicit cast to uint64_t upon failure of ceph_statfs

vfs_ceph: explicit cast to uint64_t upon failure of ceph_statfs

When a call to 'ceph_statfs' from with 'cephwrap_disk_free' returns
non-zero status do an explicit cast to uint64_t for the negative (-1)
value returned by 'status_code'.

Signed-off-by: Shachar Sharon <ssharon@redhat.com>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Reviewed-by: Anoop C S <anoopcs@samba.org>