leds: triggers: Constify 'struct bin_attribute'

The sysfs core now allows instances of 'struct bin_attribute' 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/20241222-sysfs-const-bin_attr-led-v1-1-ecc5212a31fa@weissschuh.net


Signed-off-by: Lee Jones <lee@kernel.org>