[AVR,CSKY] Migrate away from MCValue::getSymB

The MCValue::SymB MCSymbolRefExpr member might be replaced with a
MCSymbol in the future. Reduce direct access.

Author: MaskRay

llvm/lib/Target/AVR/MCTargetDesc/AVRMCExpr.cpp

@@ -85,12 +85,13 @@ bool AVRMCExpr::evaluateAsRelocatableImpl(MCValue &Result,
     MCSymbolRefExpr::VariantKind Modifier = Sym->getKind();
     if (Modifier != MCSymbolRefExpr::VK_None)
       return false;
+    assert(!Value.getSubSym());
     if (specifier == VK_PM) {
       Modifier = MCSymbolRefExpr::VariantKind(AVRMCExpr::VK_PM);
     }
 
     Sym = MCSymbolRefExpr::create(&Sym->getSymbol(), Modifier, Context);
-    Result = MCValue::get(Sym, Value.getSymB(), Value.getConstant());
+    Result = MCValue::get(Sym, nullptr, Value.getConstant());
   }
 
   return true;

llvm/lib/Target/CSKY/MCTargetDesc/CSKYMCExpr.cpp

@@ -72,5 +72,5 @@ bool CSKYMCExpr::evaluateAsRelocatableImpl(MCValue &Res,
   if (!getSubExpr()->evaluateAsRelocatable(Res, Asm))
     return false;
   Res.setSpecifier(specifier);
-  return !Res.getSymB();
+  return !Res.getSubSym();
 }