drm/i915: fix panel unlock register mask

Use the correct mask for the unlock bits. In theory this could have lead
to incorrect asserts but this is unlikely in practise.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -1210,7 +1210,7 @@ static void assert_panel_unlocked(struct drm_i915_private *dev_priv,
 
 	val = I915_READ(pp_reg);
 	if (!(val & PANEL_POWER_ON) ||
-	    ((val & PANEL_UNLOCK_REGS) == PANEL_UNLOCK_REGS))
+	    ((val & PANEL_UNLOCK_MASK) == PANEL_UNLOCK_REGS))
 		locked = false;
 
 	if (I915_READ(lvds_reg) & LVDS_PIPEB_SELECT)