The fact it isn't marked as stealing, and the fact the bed is no longer owned, seems to imply it's your room once you're named the new Harbinger.
Actually I was talking about right after he's killed, and before the funeral/Ysgramor's tomb and being named harbinger. When you're just going into his room to retrieve the last fragment, it's all still marked as "steal" (except for the fragment and gem, and books in the outer room).
I've never gone back to his room after being named, I'll have to try that.
I was very moved by the journal, tho.