drm/amd/display: should check error using DC_OK

core_link_read_dpcd returns only DC_OK(1) and DC_ERROR_UNEXPECTED(-1),
the caller should check error using DC_OK instead of checking against 0
Signed-off-by: Tong Zhang <ztong0001@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c

@@ -4409,9 +4409,9 @@ bool dc_link_get_backlight_level_nits(struct dc_link *link,
 			link->connector_signal != SIGNAL_TYPE_DISPLAY_PORT))
 		return false;
 
-	if (!core_link_read_dpcd(link, DP_SOURCE_BACKLIGHT_CURRENT_PEAK,
+	if (core_link_read_dpcd(link, DP_SOURCE_BACKLIGHT_CURRENT_PEAK,
 			dpcd_backlight_get.raw,
-			sizeof(union dpcd_source_backlight_get)))
+			sizeof(union dpcd_source_backlight_get)) != DC_OK)
 		return false;
 
 	*backlight_millinits_avg =
@@ -4450,9 +4450,9 @@ bool dc_link_read_default_bl_aux(struct dc_link *link, uint32_t *backlight_milli
 		link->connector_signal != SIGNAL_TYPE_DISPLAY_PORT))
 		return false;
 
-	if (!core_link_read_dpcd(link, DP_SOURCE_BACKLIGHT_LEVEL,
+	if (core_link_read_dpcd(link, DP_SOURCE_BACKLIGHT_LEVEL,
 		(uint8_t *) backlight_millinits,
-		sizeof(uint32_t)))
+		sizeof(uint32_t)) != DC_OK)
 		return false;
 
 	return true;