Broadcast radio 1.x default implementation: let's support background scan.

Bug: 69860743
Test: VTS
Change-Id: I7f0dc841e2b3fc218e5e7efa9b102697655cc9d5
diff --git a/broadcastradio/1.2/default/Tuner.cpp b/broadcastradio/1.2/default/Tuner.cpp
index f589332..e95a132 100644
--- a/broadcastradio/1.2/default/Tuner.cpp
+++ b/broadcastradio/1.2/default/Tuner.cpp
@@ -343,7 +343,11 @@
     lock_guard<mutex> lk(mMut);
     if (mIsClosed) return ProgramListResult::NOT_INITIALIZED;
 
-    return ProgramListResult::UNAVAILABLE;
+    if (mCallback1_1 != nullptr) {
+        mCallback1_1->backgroundScanComplete(ProgramListResult::OK);
+    }
+
+    return ProgramListResult::OK;
 }
 
 Return<void> Tuner::getProgramList(const hidl_vec<VendorKeyValue>& vendorFilter,