drm/amd/display: Add null check to dc_submit_i2c_oem

[why]
dc_submit_i2c_oem could be called with ddc null

[how]
add null check and fail the call instead
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Martin Leung <martin.leung@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/core/dc.c

@@ -3477,10 +3477,13 @@ bool dc_submit_i2c_oem(
 		struct i2c_command *cmd)
 {
 	struct ddc_service *ddc = dc->res_pool->oem_device;
-	return dce_i2c_submit_command(
-		dc->res_pool,
-		ddc->ddc_pin,
-		cmd);
+	if (ddc)
+		return dce_i2c_submit_command(
+			dc->res_pool,
+			ddc->ddc_pin,
+			cmd);
+
+	return false;
 }
 
 static bool link_add_remote_sink_helper(struct dc_link *dc_link, struct dc_sink *sink)