esp_eth: Fix w5500 to correctly read registers on -Os
esp_eth: Fix w5500 to correctly read registers on -Os

Reading SPI data may come in 4-byte units and thus result in unwanted
overwrites if smaller size registers read, especially if multiple placed
one after another. Fixed by using direct reads to `trans` structure for
sizes smaller or equal to 4.

Closes https://github.com/espressif/esp-idf/issues/6579

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf