zte: plug memleak

The GError wasn't properly disposed.

Reported by: Ben Chan <benchan@google.com>

plugins/zte/mm-broadband-modem-zte.c

@@ -96,9 +96,13 @@ cpms_try_ready (MMBaseModem *self,
                          MM_MOBILE_EQUIPMENT_ERROR_SIM_BUSY)) {
             /* Retry in 2 seconds */
         g_timeout_add_seconds (2, (GSourceFunc)cpms_timeout_cb, ctx);
+        g_error_free (error);
         return;
     }
 
+    if (error)
+        g_error_free (error);
+
     /* Well, we're done */
     g_simple_async_result_set_op_res_gboolean (ctx->result, TRUE);
     modem_after_sim_unlock_context_complete_and_free (ctx);