[MLIR] Add missing MLIRLLVMDialect dep to MLIRControlFlowToSCF

This fixes the following failure when doing a clean build (in particular
no .ninja* lying around) of lib/libMLIRControlFlowToSCF.a only:
```
In file included from llvm/include/llvm/IR/Module.h:22,
                 from mlir/include/mlir/Dialect/LLVMIR/LLVMDialect.h:37,
                 from mlir/lib/Conversion/ControlFlowToSCF/ControlFlowToSCF.cpp:19
llvm/include/llvm/IR/Attributes.h:90:14: fatal error: llvm/IR/Attributes.inc: No such file or directory
```

mlir/lib/Conversion/ControlFlowToSCF/CMakeLists.txt

@@ -12,6 +12,7 @@ add_mlir_conversion_library(MLIRControlFlowToSCF
   MLIRArithDialect
   MLIRControlFlowDialect
   MLIRFuncDialect
+  MLIRLLVMDialect
   MLIRSCFDialect
   MLIRUBDialect
   MLIRPass