drm/i915: Really ignore long HPD pulses on eDP

Return IRQ_HANDLED from intel_dp_hpd_pulse() to properly
ignore the long HPD pulse on eDP to avoid the never ending
VDD off->HPD->VDD on->VDD off->HPD... cycle.

This fixes a regression intoduced by
 commit b2c5c181
 Author: Daniel Vetter <daniel.vetter@ffwll.ch>
 Date:   Fri Jan 23 06:00:31 2015 +0100

    drm/i915: Use symbolic irqreturn for ->hpd_pulse

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -4431,7 +4431,7 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
 		 */
 		DRM_DEBUG_KMS("ignoring long hpd on eDP port %c\n",
 			      port_name(intel_dig_port->port));
-		return false;
+		return IRQ_HANDLED;
 	}
 
 	DRM_DEBUG_KMS("got hpd irq on port %c - %s\n",