[mlir][spirv] fix Bazel build of Passes.h

I cannot repro this with CMake, but on Bazel this is failing with
```
error: incomplete result type 'mlir::spirv::TargetEnvAttr' in function definition
[...]
note: in instantiation of member function 'std::function<mlir::spirv::TargetEnvAttr (mlir::spirv::ModuleOp)>::function' requested here
createUnifyAliasedResourcePass(GetTargetEnvFn getTargetEnv = nullptr);
```

Reviewed By: antiagainst

Differential Revision: https://reviews.llvm.org/D136909