Possible typo in maximal frequency.

[matoushybl]

There are two different frequencies mentioned in the comments and in the code.

https://github.com/stm32-rs/stm32f7xx-hal/blob/0a0d06d5f63c3a1471362370fdfb8c367207d308/src/rcc.rs#L468-L476

[hannobraun]

Thank you, good catch! Just from reading the code, it's not clear to me whether this is actually wrong, but it definitely looks dubious.

Even it this doesn't need fixing, a better comment would be great.

[matoushybl]

Oh, I see it now. Sorry for the mistake, I agree with adding a slightly improved comment, but I believe we could also extract the frequencies for example to a module with constants.