login: suspend - be a bit more explicit when logging

When the Suspend method is called, the only log message we write
(unless debugging is enabled) is "Operation finished.". This is
not very helpful when trying to figure out what is going on, so
add what operation we are talking about to the message:
"Operation 'sleep' finished.".

Hat tip to Daniel Aleksandersen for pointing this out.

src/login/logind-dbus.c

@@ -2588,7 +2588,7 @@ int match_job_removed(sd_bus_message *message, void *userdata, sd_bus_error *err
         }
 
         if (m->action_job && streq(m->action_job, path)) {
-                log_info("Operation finished.");
+                log_info("Operation '%s' finished.", inhibit_what_to_string(m->action_what));
 
                 /* Tell people that they now may take a lock again */
                 send_prepare_for(m, m->action_what, false);