linux-imx

libnvdimm, pmem: kill pmem->ndns

We can derive the common namespace from other information.  We also do
not need to cache it because all the usages are in slow paths.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>