[ms-inline asm] Simplify the logic by using parsePrimaryExpr.  No functional
change intended.  Test case previously added in r178568.
Part of rdar://13611297

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179425 91177308-0d34-0410-b5e6-96231b3b80d8