e1000e: reduce scope of some variables, remove unnecessary ones

Static analysis of the driver code found some variables for which the scope
can be reduced, or remove the variable altogether.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>