AMD RX470 - Speed only 580 hashes/r
Hi, i seem to get low speeds using XMRIG AMD:
![image](https://user-images.githubusercontent.com/25494601/33417975-5b5329e4-d5ac-11e7-856d-19806f37f62b.png)


I normally get 650 hashes/s with Claymore or SGMiner  - so about 1900 hashes for 3 cards with 4GB ram.

Is this a known issue 