onRegistrationImpl: handle getTransport error

Return an error instead of aborting outright, in case the calling code
has any more error logging/info/etc...

Bug: 175342959
Test: boot
Change-Id: If6066a3dded8b916c2a1163f79e10ac527afe774
diff --git a/transport/ServiceManagement.cpp b/transport/ServiceManagement.cpp
index 8122324..08715cb 100644
--- a/transport/ServiceManagement.cpp
+++ b/transport/ServiceManagement.cpp
@@ -901,7 +901,13 @@
 
     if (kEnforceVintfManifest && !isTrebleTestingOverride()) {
         using Transport = IServiceManager1_0::Transport;
-        Transport transport = sm->getTransport(descriptor, name);
+        Return<Transport> transport = sm->getTransport(descriptor, name);
+
+        if (!transport.isOk()) {
+            LOG(ERROR) << "Could not get transport for " << descriptor << "/" << name << ": "
+                       << transport.description();
+            return UNKNOWN_ERROR;
+        }
 
         if (transport != Transport::HWBINDER) {
             LOG(ERROR) << "Service " << descriptor << "/" << name