Fixed an assertion failure related to bitfield lowering.

When lowering a bitfield, CGRecordLowering would assign the wrong 
storage type to a bitfield in some cases and trigger an assertion.  In 
these cases the layout was still correct, just the bitfield info was 
wrong.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202562 91177308-0d34-0410-b5e6-96231b3b80d8