[InstrProf] Fix build error in Correlator class

[ellis]

Summary

For some reason this did not fail to compile for me locally, but did
fail on one of the builders. Here is the error:

https://lab.llvm.org/buildbot/#/builders/58/builds/14969

/home/buildbot/as-builder-4/lld-x86_64-ubuntu-fast/llvm-project/llvm/lib/ProfileData/InstrProfCorrelator.cpp: In static member function ‘static llvm::Expected<std::unique_ptr<llvm::InstrProfCorrelator::Context> > llvm::InstrProfCorrelator::Context::get(std::unique_ptr<llvm::MemoryBuffer>, const llvm::object::ObjectFile&)’:
/home/buildbot/as-builder-4/lld-x86_64-ubuntu-fast/llvm-project/llvm/lib/ProfileData/InstrProfCorrelator.cpp:44:10: error: could not convert ‘C’ from ‘std::unique_ptr<llvm::InstrProfCorrelator::Context>’ to ‘llvm::Expected<std::unique_ptr<llvm::InstrProfCorrelator::Context> >’
   return C;

llvm/lib/ProfileData/InstrProfCorrelator.cpp

InstrProfCorrelator::Context::get(std::unique_ptr<MemoryBuffer> Buffer,
   auto CountersSection = getCountersSection(Obj);
   if (auto Err = CountersSection.takeError())
     return std::move(Err);
   auto C = std::make_unique<Context>();
   C->Buffer = std::move(Buffer);
   C->CountersSectionStart = CountersSection->getAddress();
   C->CountersSectionEnd = C->CountersSectionStart + CountersSection->getSize();
   C->ShouldSwapBytes = Obj.isLittleEndian() != sys::IsLittleEndianHost;
-  return C;
+  return Expected<std::unique_ptr<Context>>(std::move(C));
 }
 
 llvm::Expected<std::unique_ptr<InstrProfCorrelator>>
 InstrProfCorrelator::get(StringRef DebugInfoFilename) {
   auto DsymObjectsOrErr =
       object::MachOObjectFile::findDsymObjectMembers(DebugInfoFilename);
   if (auto Err = DsymObjectsOrErr.takeError())
     return std::move(Err);