policy: Fix a typo when validating the list of policies (#13735)
policy: Fix a typo when validating the list of policies (#13735)

When assigning two policies to a user using mc command, the server code
wrongly validates due to a typo in the code, the commit fixes it.

balamurugana/minio,vadmeste/minio,donatello/minio,donatello/minio,minio/minio,vadmeste/minio,minio/minio,krisis/minio,krisis/minio,balamurugana/minio