BitcodeReader::popValue - pass SmallVectorImpl<> as const reference. NFCI.

Fixes cppcheck warning.

Author: RKSimon

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -676,7 +676,7 @@ class BitcodeReader : public BitcodeReaderBase, public GVMaterializer {
   /// Read a value out of the specified record from slot 'Slot'. Increment Slot
   /// past the number of slots used by the value in the record. Return true if
   /// there is an error.
-  bool popValue(SmallVectorImpl<uint64_t> &Record, unsigned &Slot,
+  bool popValue(const SmallVectorImpl<uint64_t> &Record, unsigned &Slot,
                 unsigned InstNum, Type *Ty, Value *&ResVal) {
     if (getValue(Record, Slot, InstNum, Ty, ResVal))
       return true;