vfs_ceph: adjust code-style of cephwrap_disk_free

vfs_ceph: adjust code-style of cephwrap_disk_free

The common convention in 'vfs_ceph.c' module is to bailout (by return or
goto) whenever the return value from libcephfs call is not OK. Apply
this code-style to cephwrap_disk_free hook.

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>