examples/protocols: fix compilation when CONFIG_EXAMPLE_USE_OPENETH=y

The code checked CONFIG_ETH_USE_SPI_ETHERNET (which is usually set),
but CONFIG_EXAMPLE_ETH_SPI_xxx_GPIO options are only defined if
CONFIG_EXAMPLE_USE_SPI_ETHERNET is set. Fix the ifdef accordingly.
Regression from aea901f0.

examples/common_components/protocol_examples_common/connect.c

@@ -398,7 +398,7 @@ static esp_netif_t *eth_start(void)
 #elif CONFIG_EXAMPLE_ETH_PHY_DP83848
     s_phy = esp_eth_phy_new_dp83848(&phy_config);
 #endif
-#elif CONFIG_ETH_USE_SPI_ETHERNET
+#elif CONFIG_EXAMPLE_USE_SPI_ETHERNET
     gpio_install_isr_service(0);
     spi_device_handle_t spi_handle = NULL;
     spi_bus_config_t buscfg = {