Fix peripheral config for feature "h7b3"

[cracksalad]

Fixes #100

Although this builds with the quick start, I am not sure if it actually works. I will test it as soon as I find some time.

[David-OConnor]

Sounds good! I can merge now, or wait until you test.

[cracksalad]

I am always getting ERROR probe_rs::architecture::arm::core::armv7m: The core is in locked up status as a result of an unrecoverable exception.
I tried to use probe-rs with this memory.x config. Additionally I tried using the STM32CubeProgrammer. Both lead to the locked up core.
On the other hand I am able to flash the demo application from ST using STM32CubeIDE successfully.

So this PR helps, but does not completly fix the H7B3/H7A3 series compatibility, I think.

@David-OConnor any idea on what I could try next?
If you like to take the improvement without a complete solution anyways, feel free to merge.