kyber: constify sysfs attributes

The elevator core now allows instances of 'struct elv_fs_entry' to be
moved into read-only memory. Make use of that to protect them against
accidental or malicious modifications.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20250102-sysfs-const-attr-elevator-v1-4-9837d2058c60@weissschuh.net


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