ixgbevf: Minor cleanups

Make some minor cleanups, such as simplifying return paths, deleting
unneeded initializations, return values more directly and so forth.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Darin Miller <darin.j.miller@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>