ceph: allow copy_file_range when src and dst inode are same

There is no reason to prevent this. The OSD should be able to handle
this as long as the objects are different, and the existing code falls
back when the offset into the object is different.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Luis Henriques <lhenriques@suse.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>