drm/i915: fixup interlaced support on ilk+

According to Paulo Zanoni, this is what windows does.
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Alfonso Fiore <alfonso.fiore@gmail.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -5975,7 +5975,7 @@ static int ironlake_crtc_mode_set(struct drm_crtc *crtc,
 
 	pipeconf &= ~PIPECONF_INTERLACE_MASK;
 	if (adjusted_mode->flags & DRM_MODE_FLAG_INTERLACE) {
-		pipeconf |= PIPECONF_INTERLACE_W_FIELD_INDICATION;
+		pipeconf |= PIPECONF_INTERLACED_ILK;
 		/* the chip adds 2 halflines automatically */
 		adjusted_mode->crtc_vtotal -= 1;
 		adjusted_mode->crtc_vblank_end -= 1;