libnvdimm: prevent nvdimm from requesting key when security is disabled

Current implementation attempts to request keys from the keyring even when
security is not enabled. Change behavior so when security is disabled it
will skip key request.

Error messages seen when no keys are installed and libnvdimm is loaded:

    request-key[4598]: Cannot find command to construct key 661489677
    request-key[4606]: Cannot find command to construct key 34713726

Cc: stable@vger.kernel.org
Fixes: 4c6926a2 ("acpi/nfit, libnvdimm: Add unlock of nvdimm support for Intel DIMMs")
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/156934642272.30222.5230162488753445916.stgit@djiang5-desk3.ch.intel.com


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