[FIRRTL][EmitOMIR] Don't insert above pass level.

[dtzSiFive]

Since EmitOMIR is a firrtl::CircuitOp pass, don't attempt to acccess or modify or insert into the operation above the one the pass is running on.

[mikeurbach]

It makes sense not to emit things outside the operation the pass is running on. After LowerToHW and ExportVerilog, do these verbatims still get emitted correctly? That would be my only concern.

[uenoku]

LGTM, I believe verbatim op won't be erased by LowerToHW.

[dtzSiFive]

If we need to insert outside the circuit, we can make this a ModuleOp pass (like CreateSiFiveMetadata).

And yeah LowerToHW will make these siblings of the hw.module operations (and others) that it creates.

[dtzSiFive]

Thanks for the review!