[Codegen][NFC] Replace 'RegisterRegAlloc::FunctionPassCtor'

with 'RegisterRegAllocBase<T>::FunctionPassCtor'.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D145032

llvm/include/llvm/CodeGen/RegAllocRegistry.h

@@ -66,7 +66,7 @@ class RegisterRegAlloc : public RegisterRegAllocBase<RegisterRegAlloc> {
 
 /// RegisterRegAlloc's global Registry tracks allocator registration.
 template <class T>
-MachinePassRegistry<RegisterRegAlloc::FunctionPassCtor>
+MachinePassRegistry<typename RegisterRegAllocBase<T>::FunctionPassCtor>
 RegisterRegAllocBase<T>::Registry;
 
 } // end namespace llvm