drm/amd/display: Added local_sink null check before access

[Why & How]
Need to check if local_sink is NULL before accessing.
Signed-off-by: Jake Wang <haonan.wang2@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -167,7 +167,8 @@ bool edp_receiver_ready_T9(struct dc_link *link)
 		} while (++tries < 50);
 	}
 
-	if (link->local_sink->edid_caps.panel_patch.extra_delay_backlight_off > 0)
+	if (link->local_sink &&
+			link->local_sink->edid_caps.panel_patch.extra_delay_backlight_off > 0)
 		udelay(link->local_sink->edid_caps.panel_patch.extra_delay_backlight_off * 1000);
 
 	return result;
@@ -201,7 +202,8 @@ bool edp_receiver_ready_T7(struct dc_link *link)
 		} while (time_taken_in_ns < 50 * 1000000); //MAx T7 is 50ms
 	}
 
-	if (link->local_sink->edid_caps.panel_patch.extra_t7_ms > 0)
+	if (link->local_sink &&
+			link->local_sink->edid_caps.panel_patch.extra_t7_ms > 0)
 		udelay(link->local_sink->edid_caps.panel_patch.extra_t7_ms * 1000);
 
 	return result;