That would be Mwanaume wa Uholanzi, i.e. Man of Holland. The word mholanzi by itself actually means 'Dutchman'. so, the literal translation of Mwanaume wa mholanzi would be 'Man of Dutchman'. My suspicion is that Mwanaume mholanzi is just plainly wrong, but I'm not all certain about that.
[EDIT] Just got confirmed from a native speaker that Mwanaume wa Uholanzi is the correct translation of 'A Dutch Man'