Adjust RIG_BACKEND_NUM in register.c so it can detect bad rig numbers

https://github.com/Hamlib/Hamlib/issues/735

src/register.c

@@ -259,8 +259,8 @@ static int rig_lookup_backend(rig_model_t rig_model)
 
     for (i = 0; i < RIG_BACKEND_MAX && rig_backend_list[i].be_name; i++)
     {
-        if (RIG_BACKEND_NUM(rig_model) ==
-                rig_backend_list[i].be_num)
+        if (rig_model ==
+                rig_backend_list[i].be_num*1000)
         {
             return i;
         }