device-dax: Properly handle drivers without remove callback

If all resources are allocated in .probe() using devm_ functions it
might make sense to not provide a .remove() callback. Then the right
thing is to just return success.

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Link: https://lore.kernel.org/r/20210205222842.34896-3-uwe@kleine-koenig.org


Signed-off-by: Dan Williams <dan.j.williams@intel.com>