Merging r262577:

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r262577 | thomas.stellard | 2016-03-02 19:45:09 -0800 (Wed, 02 Mar 2016) | 12 lines

AMDGPU/SI: Don't try to move scratch wave offset when there are no free SGPRs

Summary:
When there were no free SGPRs, we were trying to move this value into
some of the reserved registers which was causing a segmentation fault.

Reviewers: arsenm

Subscribers: arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D17590

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llvm-svn: 271720