Change NoHwServiceManager to return EMPTY instead of PASSTHROUGH

Transport::EMPTY makes more sense than Transport::PASSTHROUGH when there
is no hwservicemanager installed on a device.

Test: m
Bug: none
Change-Id: I8c5b0ec600eb6ece9a11dc91a42196bb6b764494
diff --git a/transport/ServiceManagement.cpp b/transport/ServiceManagement.cpp
index f3ee611..637e74b 100644
--- a/transport/ServiceManagement.cpp
+++ b/transport/ServiceManagement.cpp
@@ -240,7 +240,7 @@
     Return<Transport> getTransport(const hidl_string& fqName, const hidl_string& name) {
         LOG(INFO) << "Trying to get transport of " << fqName << "/" << name
                   << " without hwservicemanager";
-        return Transport::PASSTHROUGH;
+        return Transport::EMPTY;
     }
 
     Return<void> list(list_cb _hidl_cb) override {