AMDGPU/GFX10: fix scratch resource descriptor

Summary:
The stride should depend on the wave size, not the hardware generation.

Also, the 32_FLOAT format is 0x16, not 16; though that shouldn't be
relevant.

Change-Id: I088f93bf6708974d085d1c50967f119061da6dc6

Reviewers: arsenm, rampitec, mareko

Subscribers: kzhuravl, jvesely, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63808

llvm-svn: 364788