AMDGPU: Fix SDWA peephole for V_AND_B32

Summary:
Found by inspection. We care about the operand that *doesn't*
contain the immediate.

I believe this is currently not hit because we fold 0xff / 0xffff
immediates only later.

Change-Id: Ic3cf8538bc7da5eff3200d96eccf9d339e6345a7

Reviewers: arsenm, rampitec

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

Differential Revision: https://reviews.llvm.org/D45886

llvm-svn: 330586