[PATCH] [ARM] Fix an assertion failure in A15SDOptimizer about DPair reg class

[Tim Northover]

Hi Hao,

> There are two ways to fix this, one is to do nothing just return directly for
> DPair, another way is to treat DPair as QPR. I think the latter is better
> according to the purpose of this pass (To get a better register allocation
> result). So this patch treats DPair just like QPR.

I agree. The patch looks good to me.

Cheers.

Tim.