util: Fix virStorageBackendSCSINewLun error handling

Commit a523770c3 added @retval return processing for
virStorageBackendUpdateVolInfo in order to allow a -2
to be return; however, upon successful completion
@retval = 0 and if either the virStorageBackendSCSISerial
or the virStoragePoolObjAddVol failed, the method would
return 0, but not add the @vol to the pool. So let's
just reset retval = -1 and continue processing.

Signed-off-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/storage/storage_util.c

@@ -3869,6 +3869,9 @@ virStorageBackendSCSINewLun(virStoragePoolObjPtr pool,
                                                  VIR_STORAGE_VOL_READ_NOERROR)) < 0)
         goto cleanup;
 
+    /* Reset retval for proper error handling */
+    retval = -1;
+
     vol->key = virStorageBackendSCSISerial(vol->target.path,
                                            (def->source.adapter.type ==
                                             VIR_STORAGE_ADAPTER_TYPE_FC_HOST));