Damn you Mogh!
Just noticed Bror might also have the ring as well as Thorin (so there is no clear solution?).
Bror is always a liar, we only don't know if Thorin or Dekar is one but if one of them is the other one is not. And in both cases, one time Thorin is liar and one time Dekar is liar, we have a logical conclusion.
If Thorin is the liar he likes himself. Because Dekar isn't a liar he likes Bror and Thorin, so it's right that Thorin is lying about Dekar doesn't like Bror. And because Bror is lying (thus likes himself) he likes those who like themselves (Thorin and himself) and doesn't like those don't (only Dekar). If we know that Thorin is lying about more than one dwarf likes Dekar it's actually only one likes Dekar and because Bror and Dekar himself don't like Dekar it must be Thorin. Dekar is telling the truth and Thorin is the only one being liked by all and has the ring. He is lying that he doesn't haveone.
If Throin now is telling the truth (I will do it short) then he doesn't have the ring. After further conclusion (Bror is still lying) know that Dekar doesn't have the ring, because he is liked by everyone including himself because he is a liar and thus the "the one who is liked by everyone has the ring"statement is wrong (the guy that is liked by everyone doesn't have the ring if that's the true lying version of it). So only Bror can have the ring.
I have too much free time right now