attitude_estimator_ekf: use degrees for ATT_MAG_DECL parameter to be consistent with documentation

src/modules/attitude_estimator_ekf/attitude_estimator_ekf_params.c

@@ -113,6 +113,7 @@ int parameters_update(const struct attitude_estimator_ekf_param_handles *h, stru
 	param_get(h->yaw_off, &(p->yaw_off));
 
 	param_get(h->mag_decl, &(p->mag_decl));
+	p->mag_decl *= M_PI / 180.0f;
 
 	param_get(h->acc_comp, &(p->acc_comp));