only last register of ShiftRegister can be renamed by suggestName

**Type of issue**: bug report
**Impact**: no functional change

**Development Phase**: request

**If the current behavior is a bug, please provide the steps to reproduce the problem:**
https://scastie.scala-lang.org/BUm3SiiCTA6DRLi9b51YPQ

**What is the current behavior?**
`suggestName` only rename last register.

**What is the expected behavior?**
`suggestName` should rename all register generated by `ShiftRegister`

Start with the linked Scastie reproduction and inspect the ShiftRegister implementation and its suggestName behavior. Confirm why only the final generated register is renamed; done means every register generated by ShiftRegister receives the suggested name without changing functionality.

Written by the indexing model from the issue text.