npl/riot: adapt to xtimer API change
diff --git a/porting/npl/riot/include/nimble/nimble_npl_os.h b/porting/npl/riot/include/nimble/nimble_npl_os.h
index 67eb74e..61c1ea8 100644
--- a/porting/npl/riot/include/nimble/nimble_npl_os.h
+++ b/porting/npl/riot/include/nimble/nimble_npl_os.h
@@ -209,7 +209,7 @@
 static inline bool
 ble_npl_callout_is_active(struct ble_npl_callout *c)
 {
-    return (c->timer.target || c->timer.long_target);
+    return (c->timer.offset || c->timer.long_offset);
 }
 
 static inline ble_npl_time_t