drm/i915/sdvo: Constify mapping structs

We aren't intending to mutate the SDVO device mapping structs,
so make them const.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230829113920.13713-13-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_sdvo.c

@@ -2576,7 +2576,7 @@ intel_sdvo_select_ddc_bus(struct intel_sdvo *sdvo,
 			  struct intel_sdvo_connector *connector)
 {
 	struct drm_i915_private *dev_priv = to_i915(sdvo->base.base.dev);
-	struct sdvo_device_mapping *mapping;
+	const struct sdvo_device_mapping *mapping;
 	int ddc_bus;
 
 	if (sdvo->base.port == PORT_B)
@@ -2599,7 +2599,7 @@ static void
 intel_sdvo_select_i2c_bus(struct intel_sdvo *sdvo)
 {
 	struct drm_i915_private *dev_priv = to_i915(sdvo->base.base.dev);
-	struct sdvo_device_mapping *mapping;
+	const struct sdvo_device_mapping *mapping;
 	u8 pin;
 
 	if (sdvo->base.port == PORT_B)
@@ -2644,7 +2644,7 @@ static u8
 intel_sdvo_get_slave_addr(struct intel_sdvo *sdvo)
 {
 	struct drm_i915_private *dev_priv = to_i915(sdvo->base.base.dev);
-	struct sdvo_device_mapping *my_mapping, *other_mapping;
+	const struct sdvo_device_mapping *my_mapping, *other_mapping;
 
 	if (sdvo->base.port == PORT_B) {
 		my_mapping = &dev_priv->display.vbt.sdvo_mappings[0];