drm/i915: 830M doesn't have an LVDS port

There's no LVDS port on 830M so don't go reading the LVDS control
register.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -7974,7 +7974,7 @@ static void i9xx_crtc_clock_get(struct intel_crtc *crtc,
 		else
 			i9xx_clock(refclk, &clock);
 	} else {
-		u32 lvds = I915_READ(LVDS);
+		u32 lvds = IS_I830(dev) ? 0 : I915_READ(LVDS);
 		bool is_lvds = (pipe == 1) && (lvds & LVDS_PORT_EN);
 
 		if (is_lvds) {