ixgbe: Drop unnecessary adapter->hw dereference in loopback test setup

This patch drops a set of unnecessary dereferences to the hardware structure
since we already have a local copy of the hardware pointer.

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>