Assert that the offset in MachineLocation::set() is always 0. (NFC)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309818 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MachineLocation.h

@@ -67,6 +67,7 @@ public:
     IsRegister = false;
     Register = R;
     Offset = O;
+    assert(O == 0 && "offset is expected to always be zero");
   }
 };