MAINTAINERS: add Benno Lossin as Rust reviewer

MAINTAINERS: add Benno Lossin as Rust reviewer

Benno has been involved with the Rust for Linux project for
the better part of a year now. He has been working on solving
the safe pinned initialization problem [1], which resulted in
the pin-init API patch series [2] that allows to reduce the
need for `unsafe` code in the kernel. He is also working on
the field projection RFC for Rust [3] to bring pin-init as
a language feature.

His expertise with the language will be very useful to have
around in the future if Rust grows within the kernel, thus
add him to the `RUST` entry as reviewer.

Link: https://rust-for-linux.com/the-safe-pinned-initialization-problem
Link: https://lore.kernel.org/rust-for-linux/20230408122429.1103522-1-y86-dev@protonmail.com/
Link: https://github.com/rust-lang/rfcs/pull/3318
Cc: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alex Gaynor <alex.gaynor@gmail.com>
Link: https://lore.kernel.org/r/20230412221823.830135-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>