ixgbe: Make return values more direct

Make return values more direct, eliminating some gotos and
otherwise unneeded conditionals. This also eliminates some
local variables. Also a few minor cleanups in affected code
so checkpatch won't complain.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>