Disable misguided clippy lint

[jannic]

Disables this warning and its wrong suggestion:

warning: called `Iterator::last` on a `DoubleEndedIterator`; this will needlessly iterate the entire iterator
   --> embedded-hal-nb/src/serial.rs:127:17
    |
127 |           let _ = s
    |  _________________^
128 | |             .bytes()
129 | |             .map(|c| nb::block!(self.write(Word::from(c))))
130 | |             .last();
    | |______________-----^
    |                |
    |                help: try: `next_back()`
    |
    = note: this change will alter drop order which may be undesirable
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#double_ended_iterator_last
    = note: `#[warn(clippy::double_ended_iterator_last)]` on by default

[burrbull]

for

[Dirbaio]

IMO the real issue here is using map for the side effect (it's not idiomatic). We should fix it with a plain old for .. in instead.