libnvdimm/label: Remove the dpa align check

There's no strict requirement why slot_valid() needs to check for page alignment
and it would seem to actively hurt cross-page-size compatibility. Let's
delete the check and rely on checksum validation.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Link: https://lore.kernel.org/r/20190905154603.10349-6-aneesh.kumar@linux.ibm.com


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