Error when running the rng example on stm32l476rg

[Dueesberch]

When running example/stm32l4/src/bin/rng.rs I get

Error: Failed to attach to RTT
Caused by:
    Error attempting to attach to RTT: RTT control block not found in target memory.
    - Make sure RTT is initialized on the target, AND that there are NO target breakpoints before RTT initialization.
    - For VSCode and probe-rs-debugger users, using 'halt_after_reset:true' in your 'launch.json' file will prevent RTT
    initialization from happening on time.
    - Depending on the target, sleep modes can interfere with RTT.

That error is already described here Issue 2221, but adding config.rcc.clk48_src = Clk48Src::PLL1_Q ends in unknown field for clk48_src and use of undeclared type 'Clk48Src'