drm/amd/display: Change dc_surface_update cm2_params to const

[WHY]
cm2_params is used to set update_flags.
It's value is not intended to be modified.

[WHAT]
Change the declaration of cm2_params to be a constant variable

Reviewed-by: Tao Huang <tao.huang@amd.com>
Reviewed-by: Ariel Bernstein <eric.bernstein@amd.com>
Signed-off-by: Shunlu Zhang <Shunlu.Zhang@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc.h

@@ -1513,7 +1513,7 @@ struct dc_surface_update {
 	 * change cm2_params.component_settings: Full update
 	 * change cm2_params.cm2_luts: Fast update
 	 */
-	struct dc_cm2_parameters *cm2_params;
+	const struct dc_cm2_parameters *cm2_params;
 	const struct dc_csc_transform *cursor_csc_color_matrix;
 	unsigned int sdr_white_level_nits;
 };