Fix warnings

[usbalbin]

Fix clippy warnings

[no111u3]

@usbalbin this review partially outdated, please update if you have some ability.

[usbalbin]

warning: method `unlock_options` is never used
  --> src/flash.rs:62:8
   |
61 | impl<'a, const SECTOR_SZ_KB: u32> FlashWriter<'a, SECTOR_SZ_KB> {
   | --------------------------------------------------------------- method in this implementation
62 |     fn unlock_options(&mut self) -> Result<()> {
   |        ^^^^^^^^^^^^^^

@amcelroy , Is this function supposed to be public or is it just left as a "good to have" for features to be added later?

[no111u3]

@usbalbin please mark comments as resolved (button Resolve conversation) if you fix it, it make clear that exactly changed.

[amcelroy]

warning: method `unlock_options` is never used
  --> src/flash.rs:62:8
   |
61 | impl<'a, const SECTOR_SZ_KB: u32> FlashWriter<'a, SECTOR_SZ_KB> {
   | --------------------------------------------------------------- method in this implementation
62 |     fn unlock_options(&mut self) -> Result<()> {
   |        ^^^^^^^^^^^^^^

@amcelroy , Is this function supposed to be public or is it just left as a "good to have" for features to be added later?

It is meant to be used if someone needs it, it just isn't used for now. I did use it to test changing the flash from single to dual block, but didn't end up needing to do that.

[usbalbin]

Not sure if this is how something like this is best done...

Edit: Clarification, example/flash_with_rtic is made just for stm32g474