oci: move channel close to writer goroutine
oci: move channel close to writer goroutine

solves the crash:

goroutine 7073 [running]:
github.com/cri-o/cri-o/internal/oci.(*Runtime).WaitContainerStateStopped.func1(0xc000bda240,
0x23e36a0, 0xc000bdc030, 0xc0001b11e0, 0xc000bda1e0)
	src/github.com/cri-o/cri-o/internal/oci/oci.go:132 +0xdc
created by github.com/cri-o/cri-o/internal/oci.(*Runtime).WaitContainerStateStopped
	src/github.com/cri-o/cri-o/internal/oci/oci.go:120 +0x156

regression introduced with e8c12b348d7d6a14e99d2e1c2edbc48f1c1bf2d6

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

nalind/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/cri-o,nalind/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid,nalind/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid