ixgbe: Fix register defines to correctly handle complex expressions

This patch is meant to address possible issues with the IXGBE register
defines generating incorrect values when given a complex expression for the
register offset.

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