[ethernet] Fix SPI3_HOST default breaking compile on variants without SPI3 (#15809)

Co-authored-by: J. Nick Koston <nick@home-assistant.io>

esphome/components/ethernet/ethernet_component.h

@@ -221,7 +221,7 @@ class EthernetComponent final : public Component {
   int reset_pin_{-1};
   int phy_addr_spi_{-1};
   int clock_speed_;
-  spi_host_device_t interface_{SPI3_HOST};
+  spi_host_device_t interface_{SPI2_HOST};
 #ifdef USE_ETHERNET_SPI_POLLING_SUPPORT
   uint32_t polling_interval_{0};
 #endif

tests/components/ethernet/test.esp32-c3-idf.yaml

@@ -0,0 +1,19 @@
+ethernet:
+  type: W5500
+  clk_pin: 6
+  mosi_pin: 7
+  miso_pin: 2
+  cs_pin: 10
+  interrupt_pin: 3
+  reset_pin: 4
+  clock_speed: 10Mhz
+  manual_ip:
+    static_ip: 192.168.178.56
+    gateway: 192.168.178.1
+    subnet: 255.255.255.0
+  domain: .local
+  mac_address: "02:AA:BB:CC:DD:01"
+  on_connect:
+    - logger.log: "Ethernet connected!"
+  on_disconnect:
+    - logger.log: "Ethernet disconnected!"