libnvdimm/dimm: Simplify nvdimm_remove()

nvdimm_remove is only ever called after nvdimm_probe() returned
successfully. In this case driver data is always set to a non-NULL value
so the check for driver data being NULL can go away as it's always false.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20210212171043.2136580-1-u.kleine-koenig@pengutronix.de


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