igb: rename phy ops

This patch renames write_phy_reg to write_reg and read_phy_reg to read_reg.
It seems redundant to call out phy in an operation that is part of the
phy_ops struct.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>