Initialize pointers for vendor_interface

Default member variables to nullptr.

Bug: 118075338
Test: Inspection
Change-Id: I5fc8a5b45d2c1116036139e308743a1928abaef3
diff --git a/bluetooth/1.0/default/vendor_interface.cc b/bluetooth/1.0/default/vendor_interface.cc
index e5f02f3..d56e344 100644
--- a/bluetooth/1.0/default/vendor_interface.cc
+++ b/bluetooth/1.0/default/vendor_interface.cc
@@ -294,6 +294,7 @@
     lib_interface_->op(BT_VND_OP_POWER_CTRL, &power_state);
 
     lib_interface_->cleanup();
+    lib_interface_ = nullptr;
   }
 
   if (lib_handle_ != nullptr) {