cifs: fix potential double free during failed mount

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2088799



Cc: stable@vger.kernel.org
Signed-off-by: Roberto Bergantinos <rbergant@redhat.com>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>