[AMDGPU] Enable machine verification after AMDGPUISelDAGToDAG

[foad]

Summary

This was introduced in D32628 but it does not seem to be required any
more. At least it does not show any problems in check-llvm in an
LLVM_ENABLE_EXPENSIVE_CHECKS build.

[rampitec]

LGTM

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

 
 bool AMDGPUPassConfig::addPreISel() {
   if (TM->getOptLevel() > CodeGenOpt::None)
     addPass(createFlattenCFGPass());
   return false;
 }
 
 bool AMDGPUPassConfig::addInstSelector() {
-  // Defer the verifier until FinalizeISel.
-  addPass(createAMDGPUISelDag(&getAMDGPUTargetMachine(), getOptLevel()), false);
+  addPass(createAMDGPUISelDag(&getAMDGPUTargetMachine(), getOptLevel()));
   return false;
 }
 
 bool AMDGPUPassConfig::addGCPasses() {
   // Do nothing. GC is not supported.
   return false;
 }