i40e: use common failure flow

As mentioned by Joe Perches, we should be using
foo = alloc(...)
if (!foo)
	return -ENOMEM;

return 0;

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
CC: Joe Perches <joe@perches.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>