drm: Fix regression in disable polling e58f637b

I broke out my trusty i845 and found a new boot failure, which upon
inspection turned out to be a recursion within:

drm_helper_probe_single_connector_modes() -> drm_helper_hpd_irq_event()
-> intel_crt_detect() -> drm_helper_probe_single_connector_modes()

Calling drm_kms_helper_poll_enable() instead performs the desired
re-initialisation of the polling should the user have toggled the
parameter, without the recursive side-effect.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc_helper.c

@@ -104,7 +104,7 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
 			connector->funcs->force(connector);
 	} else {
 		connector->status = connector->funcs->detect(connector);
-		drm_helper_hpd_irq_event(dev);
+		drm_kms_helper_poll_enable(dev);
 	}
 
 	if (connector->status == connector_status_disconnected) {