libhidladapter: += vendor_available

Breaking VNDK builds.

Test: vendor modules find this.
Bug: 37518178

Change-Id: If33a71dbb0b81ab88137b6b5d3b72a769875a30e
diff --git a/adapter/Android.bp b/adapter/Android.bp
index d89b216..9bedb7b 100644
--- a/adapter/Android.bp
+++ b/adapter/Android.bp
@@ -14,6 +14,7 @@
 
 cc_library_shared {
     name: "libhidladapter",
+    vendor_available: true,
     srcs: [
         "HidlBinderAdapter.cpp"
     ],