[LoopUnrollAnalyzer] Fix a bug in UnrolledInstAnalyzer::visitLoad.

When simplifying a load we need to make sure that the type of the
simplified value matches the type of the instruction we're processing.
In theory, we can handle casts here as we deal with constant data, but
since it's not implemented at the moment, we at least need to bail out.

This fixes PR28262.

llvm-svn: 273562