Edit your /etc/hostapd/hostapd.conf file like below and restart hostapd.
#WPS stuff
# Enable control interface for PBC/PIN entry
ctrl_interface=/var/run/hostapd
eap_server=1
wps_state=2
ap_setup_locked=1
wps_pin_requests=/var/run/hostapd.pin-req
config_methods=label display push_button keypad
#WPS model info stuff change to suit your needs
device_name=USB2.0 WLAN
manufacturer=ATHEROS
model_name=WAP........