When using a Garmin GDL-52 with ForeFlight, only one ADS-B or XM weather source will be available for use. ForeFlight does not support using both weather sources at the same time. Further, there is not an option to choose which weather type will be used if you have an XM subscription for the Garmin GDL-52.
The Garmin GDL-52 will provide ADS-B data to ForeFlight unless an XM subscription is detected. Once detected, only XM weather will be available.