drm/i915/lvds: Always use 0 to disable the pfit controller

... and just any combination of bits & ~PFIT_ENABLE. This way we do not
attempt disable to the panel fitter controller uselessly upon
intel_lvds_disable().
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_lvds.c

@@ -374,6 +374,10 @@ static bool intel_lvds_mode_fixup(struct drm_encoder *encoder,
 	}
 
 out:
+	if ((pfit_control & PFIT_ENABLE) == 0) {
+		pfit_control = 0;
+		pfit_pgm_ratios = 0;
+	}
 	if (pfit_control != intel_lvds->pfit_control ||
 	    pfit_pgm_ratios != intel_lvds->pfit_pgm_ratios) {
 		intel_lvds->pfit_control = pfit_control;