This first brankie is an adjective but I don't see what the issue is with that. The second use looks like the same word but has a totally different meaning. There are lots of words like that. For instance the word 'bank' can be a noun meaning either a high street savings bank, or a piece of sloping ground, or it can be a verb in the sense of a plane banking over. There is nothing unusual about words having multiple meanings. Why should Scots words be any different. Jamieson came from my neck of the woods and no doubt did a great job but his work was not of the scope of the Scottish National Dictionary which was 70 years in the making and the CSD is a abbreviated version of that. It dates the use of "brank" as to act violently from the early 15thC. So they are not just dating that from the works of Hogg being typed incorrectly. To me it is simply saying "what makes you hide in the brush beyond the fight". I see no reason to suppose that everyone has been singing an incorrect word from a typo for the past couple of centuries. Saying that there is no reason that someone couldn't sing 'bankie-o' if they wanted!!