spi: fix the misleading example, letting the master wait until slave is ready

examples/peripherals/spi_slave/sender/main/app_main.c

@@ -152,7 +152,7 @@ void app_main()
         t.tx_buffer=sendbuf;
         t.rx_buffer=recvbuf;
         //Wait for slave to be ready for next byte before sending
-        xSemaphoreTake(rdySem, 100);//portMAX_DELAY); //Wait until slave is ready
+        xSemaphoreTake(rdySem, portMAX_DELAY); //Wait until slave is ready
         ret=spi_device_transmit(handle, &t);
         printf("Received: %s\n", recvbuf);
         n++;