net: dsa: microchip: ksz9477: use ksz_read_phy16 & ksz_write_phy16

ksz8795 and ksz9477 implementation on phy read/write hooks are
different. This patch modifies the ksz9477 implementation same as
ksz8795 by updating the ksz9477_dev_ops structure.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>