move assert back in original position

Author: Pierre-vh

llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp

@@ -2146,9 +2146,10 @@ void SIInsertWaitcnts::updateEventWaitcntAfter(MachineInstr &Inst,
       return;
     }
 
-    int FlatASCount = 0;
     assert(Inst.mayLoadOrStore());
 
+    int FlatASCount = 0;
+
     if (mayAccessVMEMThroughFlat(Inst)) {
       ++FlatASCount;
       ScoreBrackets->updateByEvent(TII, TRI, MRI, getVmemWaitEventType(Inst),