[SV Compliance][Slang] Fix nested comment syntax

[Scheremo]

Very nitpicky PR, but the System Verilog spec forbids nested block comments:
IEEE 1800-2023 Section 5.4 "Comments":

SystemVerilog has two forms to introduce comments. A one-line comment shall start with the two
characters // and end with a newline character. A block comment shall start with /* and end with /. Block
comments shall not be nested. The one-line comment token // shall not have any special meaning inside a
block comment, and the block comment tokens / and */ shall not have any special meaning inside a one-
line comment.

This PR fixes this in hwpe_stream_fifo_passthrough

[FrancescoConti]

I would be even more nitpicky and ask you to keep the second /** (it's used to auto-gen documentation with my beautiful good'ol'hack https://github.com/FrancescoConti/svprettyplot ).