Do not use '&' prefix for globals when register base field is non-zero, otherwise...

Do not use '&' prefix for globals when register base field is non-zero, otherwise msp430-as will silently miscompile the code (TI's assembler report an error though).

This fixes PR6349

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97877 91177308-0d34-0410-b5e6-96231b3b80d8