Merging r268295:

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r268295 | thomas.stellard | 2016-05-02 13:11:44 -0700 (Mon, 02 May 2016) | 7 lines

AMDGPU/SI: Use v_readfirstlane_b32 when restoring SGPRs spilled to
scratch

We were using v_readlane_b32 with the lane set to zero, but this won't
work if thread 0 is not active.

Differential Revision: http://reviews.llvm.org/D19745

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llvm-svn: 271771