[BUG] DDC forwarding

[PRugg-Cap]

Is there an existing CVA6 bug for this?

• I have searched the existing bug issues

Bug Description

CSR writes that change DDC followed soon after by instructions that read DDC as an operand (e.g. CTestSubset) see a stale value.

@jonwoodruff found this using the pipelined DII implementation, and a PR is incoming.