Fix assert when inlining a constantexpr addrspacecast

Fix assert when inlining a constantexpr addrspacecast

The pointer size of the addrspacecasted pointer might not have matched,
so this would have hit an assert in accumulateConstantOffset.

I think this was here to allow constant folding of a load of an
addrspacecasted constant. Accumulating the offset through the
addrspacecast doesn't make much sense, so something else is necessary
to allow folding the load through this cast.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243300 91177308-0d34-0410-b5e6-96231b3b80d8