drm/amd/display: remove variable "result" in dcn20_patch_unknown_plane_state()

Fix the following coccicheck warning:

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c:3216:16-22:
Unneeded variable: "result". Return "DC_OK" on line 3229
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -3255,8 +3255,6 @@ static struct dc_cap_funcs cap_funcs = {
 
 enum dc_status dcn20_patch_unknown_plane_state(struct dc_plane_state *plane_state)
 {
-	enum dc_status result = DC_OK;
-
 	enum surface_pixel_format surf_pix_format = plane_state->format;
 	unsigned int bpp = resource_pixel_format_to_bpp(surf_pix_format);
 
@@ -3268,7 +3266,7 @@ enum dc_status dcn20_patch_unknown_plane_state(struct dc_plane_state *plane_stat
 		swizzle = DC_SW_64KB_S;
 
 	plane_state->tiling_info.gfx9.swizzle = swizzle;
-	return result;
+	return DC_OK;
 }
 
 static struct resource_funcs dcn20_res_pool_funcs = {