'security' attribute displays the security state of an nvdimm.
During normal operation, the nvdimm state maybe one of 'disabled',
'unlocked' or 'locked'.  When an admin issues
  # ndctl sanitize-dimm nmem0 --overwrite
the attribute is expected to change to 'overwrite' until the overwrite
operation completes.

But tests on our systems show that 'overwrite' is never shown during
the overwrite operation. i.e.
  # cat /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/security
  unlocked
the attribute remain 'unlocked' through out the operation, consequently
"ndctl wait-overwrite nmem0" command doesn't wait at all.

The driver tracks the state in 'nvdimm->sec.flags': when the operation
starts, it adds an overwrite bit to the flags; and when the operation
completes, it removes the bit. Hence security_show() should check the
'overwrite' bit first, in order to indicate the actual state when multiple
bits are set in the flags.

Link: https://lore.kernel.org/r/1596494499-9852-2-git-send-email-jane.chu@oracle.comReviewed-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>