MAINTAINERS: add entry for Rust block device driver API

Add an entry for the Rust block device driver abstractions.

Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20240611114551.228679-4-nmi@metaspace.dk


Signed-off-by: Jens Axboe <axboe@kernel.dk>