NFC: netlink: Add result of firmware operation to completion event

Result is added as an NFC_ATTR_FIRMWARE_DOWNLOAD_STATUS attribute
containing the standard errno positive value of the completion result.
This event will be sent when the firmare download operation is done and
will contain the operation result.

Signed-off-by: Eric Lapuyade <eric.lapuyade@intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>