libnvdimm: Replace guid_copy() with import_guid() where it makes sense

There is a specific API to treat raw data as GUID, i.e. import_guid().
Use it instead of guid_copy() with explicit casting.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20200422130539.45636-1-andriy.shevchenko@linux.intel.com


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