libnvdimm, dimm: clear 'locked' status on successful DIMM enable

If we successfully enable a DIMM then it must not be locked and we can
clear the label-read failure condition. Otherwise, we need to reload the
entire bus provider driver to achieve the same effect, and that can
disrupt unrelated DIMMs and namespaces.

Fixes: 9d62ed96 ("libnvdimm: handle locked label storage areas")
Cc: <stable@vger.kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>