It possibly does mean 'friend', but in relatively recent US colloquial language, 'huckleberry' meant 'sweetheart', though in earlier times it meant 'someone of no consequence'! Earlier still, the word was used to imply something valueless. Americans seem to have used it in much the same way as we British used 'peppercorn', as in the phrase "a peppercorn rent". Perhaps it all has to do with "whispering sweet nothings"?