e1000e: Cleanup code logic in e1000_check_for_serdes_link_82571()

Cleanup code to make it more clean and readable.

Signed-off-by: Tushar Dave <tushar.n.dave@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>