Fix external radio work debug printing on removal

Fix external radio work debug printing on removal

work->type was pointing to the allocated work->ctx buffer and the debug
print in radio_work_free() ended up using freed memory if a started
external radio work was removed as part of FLUSH command operations. Fix
this by updating work->type to point to a constant string in case the
dynamic version gets freed.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>