drm/amd/display: Limit display scaling to up to 4k for DCN 3.1

[why]
The existing limit was mistakenly bigger than 4k for DCN 3.1
Reviewed-by: Zhan Liu <Zhan.Liu@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn31/dcn31_resource.c

@@ -998,7 +998,7 @@ static const struct dc_debug_options debug_defaults_drv = {
 	.disable_dcc = DCC_ENABLE,
 	.vsr_support = true,
 	.performance_trace = false,
-	.max_downscale_src_width = 7680,/*upto 8K*/
+	.max_downscale_src_width = 3840,/*upto 4K*/
 	.disable_pplib_wm_range = false,
 	.scl_reset_length10 = true,
 	.sanity_checks = false,