NFC: NCI: Signal deactivation in Target mode

Before signaling the deactivation, send a deactivation request if in
RFST_DISCOVERY state because neard assumes polling is stopped and will
try to restart it.

Signed-off-by: Julien Lefrique <lefrique@marvell.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>