drm/i915/sdvo: Only use the SDVO pin if it is in the valid range

BIOSes. Can't live without them (apparently), definitely can't live with
them.

Reported-by: Ben Gamari <bgamari@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=24312
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_sdvo.c

@@ -1908,9 +1908,12 @@ intel_sdvo_select_i2c_bus(struct drm_i915_private *dev_priv,
 		speed = mapping->i2c_speed;
 	}
 
-	sdvo->i2c = &dev_priv->gmbus[pin].adapter;
-	intel_gmbus_set_speed(sdvo->i2c, speed);
-	intel_gmbus_force_bit(sdvo->i2c, true);
+	if (pin < GMBUS_NUM_PORTS) {
+		sdvo->i2c = &dev_priv->gmbus[pin].adapter;
+		intel_gmbus_set_speed(sdvo->i2c, speed);
+		intel_gmbus_force_bit(sdvo->i2c, true);
+	} else
+		sdvo->i2c = &dev_priv->gmbus[GMBUS_PORT_DPB].adapter;
 }
 
 static bool