ixgbe: fix incorrect PHY register reads

Fix some register reads that had the opcode and register parameters swapped.
Also use define instead of a magic (0x3) number.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>