fix sse-kms context unmarshal failure (#13206)
fix sse-kms context unmarshal failure (#13206)

json.Unmarshal expects a pointer receiver, otherwise
kms.Context unmarshal fails with lack of pointer receiver,
this becomes complicated due to type aliasing over
map[string]string - fix it properly.
krisis/minio,balamurugana/minio,donatello/minio,minio/minio,donatello/minio,vadmeste/minio,vadmeste/minio,minio/minio,balamurugana/minio,krisis/minio