[ms-inline asm] Removed this unnecessary check.  In the current implementation,
Disp will always be one of MCSymbolRefExpr or MCConstantExpr, and never NULL.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180059 91177308-0d34-0410-b5e6-96231b3b80d8