Fix to use plugin instead of pointer
Fix to use plugin instead of pointer

a fix in snapshotter.go to use plugin instead of its pointer

kubernetes-incubator/external-storage,kubernetes-incubator/external-storage,childsb/external-storage,childsb/external-storage,childsb/external-storage,humblec/external-storage,kubernetes-incubator/external-storage,humblec/external-storage,humblec/external-storage