macintosh: declare ctl_table as const

Since commit 7abc9b53 ("sysctl: allow registration of const struct
ctl_table"), the sysctl registration API allows struct ctl_table variables
to be placed into read-only memory.

mac_hid_files is registered as a sysctl table and should be treated as
read-only. By declaring the mac_hid_files structure as const, we ensure
that it cannot be accidentally modified. This change improves safety.

Suggested-by: Thomas Weißschuh <linux@weissschuh.net>
Suggested-by: Ricardo B. Marliere <rbm@suse.com>
Reviewed-by: Ricardo B. Marliere <rbm@suse.com>
Signed-off-by: Luis Felipe Hernandez <luis.hernandez093@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20241217-constify_ctl_table-v1-1-402ebceaeb8e@gmail.com