drm/i915: properly clear SSC1 bit in the pch refclock init code

Noticed by staring at intel_reg_dumper diffs. Unfortunately it does
not seem to completely fix the bug.

Still, it's good to get this right, and maybe it helps someplace else.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=47117
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -5539,7 +5539,8 @@ void ironlake_init_pch_refclk(struct drm_device *dev)
 		if (intel_panel_use_ssc(dev_priv) && can_ssc) {
 			DRM_DEBUG_KMS("Using SSC on panel\n");
 			temp |= DREF_SSC1_ENABLE;
-		}
+		} else
+			temp &= ~DREF_SSC1_ENABLE;
 
 		/* Get SSC going before enabling the outputs */
 		I915_WRITE(PCH_DREF_CONTROL, temp);