Fix return logic for IMainlineSupplicant#addStaInterface.

The correct logic is to write to the object at
the provided _aidl_return pointer.

Bug: 365585450
Test: Manual test - bring up Mainline Supplicant in
      the framework and verify that addStaInterface
      returns a non-null object
Change-Id: Ied52ec8202735c792be2b2cf6ac68ef21e1aaf64
diff --git a/wpa_supplicant/aidl/mainline/mainline_supplicant.cpp b/wpa_supplicant/aidl/mainline/mainline_supplicant.cpp
index b1a873d..09021fe 100644
--- a/wpa_supplicant/aidl/mainline/mainline_supplicant.cpp
+++ b/wpa_supplicant/aidl/mainline/mainline_supplicant.cpp
@@ -52,7 +52,7 @@
     std::shared_ptr<IStaInterface> staIface =
         ndk::SharedRefBase::make<StaIface>(wpa_global_, ifaceName);
     active_sta_ifaces_[ifaceName] = staIface;
-    _aidl_return = &staIface;
+    *_aidl_return = staIface;
 
     wpa_printf(MSG_INFO, "Interface %s was added successfully", ifaceName.c_str());
     return ndk::ScopedAStatus::ok();