MC: Take MCSymbol in MachObjectWriter::getSymbolAddress(), NFC

Pass through an `MCSymbol` instead of an `MCSymbolData` so we can get
rid of the back pointer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237750 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed