Updating ose-csi-external-snapshotter builder & base images to be consistent with ART

Reconciling with https://github.com/openshift/ocp-build-data/tree/5a1293dd0f380abf50c12d65c36655486d7745d0/images/ose-csi-external-snapshotter.yml

Author: AOS Automation Release Team

Dockerfile.openshift

@@ -1,8 +1,8 @@
-FROM registry.ci.openshift.org/ocp/builder:rhel-8-golang-1.15-openshift-4.7 AS builder
+FROM registry.ci.openshift.org/ocp/builder:rhel-8-golang-1.15-openshift-4.8 AS builder
 WORKDIR /go/src/github.com/kubernetes-csi/external-snapshotter
 COPY . .
 RUN make build
 
-FROM registry.ci.openshift.org/ocp/4.7:base
+FROM registry.ci.openshift.org/ocp/4.8:base
 COPY --from=builder /go/src/github.com/kubernetes-csi/external-snapshotter/bin/csi-snapshotter /usr/bin/
 ENTRYPOINT ["/usr/bin/csi-snapshotter"]