Replace the mtd-cal-data phandle with an nvmem-cell reference for the
2.4GHz ath9k radio. This affects the following devices:
- TP-Link EAP225 v1
- TP-Link EAP225 v3
- TP-Link EAP225-Outdoor v1
- TP-Link EAP245 v1
Signed-off-by: Sander Vanheule <sander@svanheule.net>