[flang] Fix compilation after rename of Loop dialect to scf

[clementval]

Summary

Flang was not compiling correctly after the renaming of Loop dialect to SCF. This patch fixes the problem.

[ftynse]

Thanks!

flang/include/flang/Optimizer/Dialect/FIRDialect.h

 };
 
 /// Register the dialect with MLIR
 inline void registerFIR() {
   // we want to register exactly once
   [[maybe_unused]] static bool init_once = [] {
     mlir::registerDialect<mlir::AffineDialect>();
     mlir::registerDialect<mlir::LLVM::LLVMDialect>();
-    mlir::registerDialect<mlir::loop::LoopOpsDialect>();
+    mlir::registerDialect<mlir::scf::SCFDialect>();
     mlir::registerDialect<mlir::StandardOpsDialect>();
     mlir::registerDialect<mlir::vector::VectorDialect>();
     mlir::registerDialect<FIROpsDialect>();
     return true;
   }();
 }
 
 /// Register the standard passes we use. This comes from registerAllPasses(),