drm/amd/display: Avoid programming DTO if Refclk is 0

[Why]
Reference clock, either DPREFCLK or DTBCLK can be a value of 0
which then will encounter division by 0.

[How]
Avoid further calculation and programming if refclk is not
populated.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Chris Park <chris.park@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/dccg/dcn401/dcn401_dccg.c

@@ -603,6 +603,10 @@ static void dccg401_set_dp_dto(
 		BREAK_TO_DEBUGGER();
 		return;
 	}
+	if (!params->refclk_hz) {
+		BREAK_TO_DEBUGGER();
+		return;
+	}
 
 	if (!dc_is_tmds_signal(params->signal)) {
 		uint64_t dto_integer;