igc_null_write_reg
phy->ops.write_reg = igc_null_write_reg;
phy->ops.write_reg_locked = igc_null_write_reg;
phy->ops.write_reg_page = igc_null_write_reg;
s32 igc_null_write_reg(struct igc_hw *hw, u32 offset, u16 data);