Merging r295990:

------------------------------------------------------------------------
r295990 | jvesely | 2017-02-23 08:12:21 -0800 (Thu, 23 Feb 2017) | 5 lines

AMDGPU/SI: Fix trunc i16 pattern

Hit on ASICs that support 16bit instructions.

Differential Revision: https://reviews.llvm.org/D30281
------------------------------------------------------------------------

llvm-svn: 296158