firmware: google: cbmem: 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>
Acked-by: Brian Norris <briannorris@chromium.org>
Link: https://lore.kernel.org/r/20241215-sysfs-const-bin_attr-google-v1-1-e5c2808f5833@weissschuh.net


Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>