libnvdimm/security: fix a typo

libnvdimm/security: fix a typo

commit d78c620a2e82 ("libnvdimm/security: Introduce a 'frozen' attribute")
introduced a typo, causing a 'nvdimm->sec.flags' update being overwritten
by the subsequent update meant for 'nvdimm->sec.ext_flags'.

Link: https://lore.kernel.org/r/1596494499-9852-1-git-send-email-jane.chu@oracle.com
Fixes: d78c620a2e82 ("libnvdimm/security: Introduce a 'frozen' attribute")
Cc: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>