Update BoringUtils.bore to not add a port when boring from a port. (#3411)

* Update BoringUtils.bore to not add a port when boring from a port.

When drilling from the original source, if it's already a port, just
use it directly. Added a simple test from this behavior.

Also removed an errant println in the BoringUtilsSpec while updating
it.

Closes https://github.com/chipsalliance/chisel/issues/3401

.

* Updates from PR review.

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