dts: ksz8974: change port number to start at zero.
dts: ksz8974: change port number to start at zero.

Changed port numbers to start at zero since they're used as indexes
into various arrays in the code.

Signed-off-by: Arvin Farahmand <4208c8ae77e6dd3ecebee6cbd1512b26823ef0ce@ip-logix.com>

finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr