[AMDGPU] Fixed incorrect test in vcnd/vcmp optimization

This fixes a test I introduced in change D59191 (that added src0 and
src1 modifiers to the v_cndmask instruction for disassembly purposes).

Spotted by David Binderman in bug 41488.

Differential Revision: https://reviews.llvm.org/D60652

Change-Id: I6ac95e66cd84e812ed3359ad57bcd0e13198ba0c
llvm-svn: 358392