riot-rs-embassy: define_peripherals: fix type alias, allow non_camel_…

[kaspar030]

…case_types

This PR fixes setting a type alias like here.

Previously:

error: attempted to repeat an expression containing no syntax variables matched as repeating at this depth
  --> src/riot-rs-embassy/src/define_peripherals.rs:37:14
   |
37 |           $($($(
   |  ______________^
38 | |             #[allow(missing_docs)]
39 | |             pub type $peripheral_alias = peripherals::$peripheral_field;
40 | |         )?)*)*
   | |_________^

... and some non_camel_case linter warnings.