[PowerPC,MC] Replace getSymA()->getSymbol() with getAddSym. NFC

We will replace the MCSymbolRefExpr member in MCValue with MCSymbol.
This change reduces dependence on MCSymbolRefExpr.

Author: MaskRay

llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp

@@ -169,18 +169,18 @@ class PPCAsmBackend : public MCAsmBackend {
       // If the target symbol has a local entry point we must not attempt
       // to resolve the fixup directly.  Emit a relocation and leave
       // resolution of the final target address to the linker.
-      if (const MCSymbolRefExpr *A = Target.getSymA()) {
-        if (const auto *S = dyn_cast<MCSymbolELF>(&A->getSymbol())) {
+      if (const auto *A = Target.getAddSym()) {
+        if (const auto *S = dyn_cast<MCSymbolELF>(A)) {
           // The "other" values are stored in the last 6 bits of the second
           // byte. The traditional defines for STO values assume the full byte
           // and thus the shift to pack it.
           unsigned Other = S->getOther() << 2;
           if ((Other & ELF::STO_PPC64_LOCAL_MASK) != 0)
             return true;
-        } else if (const auto *S = dyn_cast<MCSymbolXCOFF>(&A->getSymbol())) {
+        } else if (const auto *S = dyn_cast<MCSymbolXCOFF>(A)) {
           return !Target.isAbsolute() && S->isExternal() &&
                  S->getStorageClass() == XCOFF::C_WEAKEXT;
-       }
+        }
       }
       return false;
     }