Move castInterface to details.

Test: pass
Test: hidl_test
Bug: 36075507
Change-Id: If801101ec77f1529691ab379d497b74357a643b7
diff --git a/generateCpp.cpp b/generateCpp.cpp
index 85a5806..7529460 100644
--- a/generateCpp.cpp
+++ b/generateCpp.cpp
@@ -1855,7 +1855,7 @@
         if (iface == superType) {
             out << "return parent;\n";
         } else {
-            out << "return ::android::hardware::castInterface<";
+            out << "return ::android::hardware::details::castInterface<";
             out << iface->localName() << ", "
                 << superType->fqName().cppName() << ", "
                 << iface->getProxyName() << ", "