virtcontainers: Ignore a staticcheck error on cpuset.go

First of all, cpuset.go just comes from kubernetes and we shouldn't be
doing much with this file apart from updating it every now and then
(but that's material for another PR).

Right now, due to some change on the static checks we use as part of our
CI, we started getting issues as:
```
INFO: Running golangci-lint on /home/fidencio/go/src/github.com/kata-containers/kata-containers/src/runtime/virtcontainers/pkg/cpuset
cpuset.go:60:2: SA4005: ineffective assignment to field Builder.done (staticcheck)
	b.done = true
```

For those, let's just ignore the lint and move on.

Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>

src/runtime/virtcontainers/pkg/cpuset/cpuset.go

@@ -57,6 +57,7 @@ func (b Builder) Add(elems ...int) {
 // Result returns the result CPUSet containing all elements that were
 // previously added to this builder. Subsequent calls to Add have no effect.
 func (b Builder) Result() CPUSet {
+	// nolint: staticcheck
 	b.done = true
 	return b.result
 }