mm/hugetlb: constify ctl_table arguments of utility functions

mm/hugetlb: constify ctl_table arguments of utility functions

The sysctl core is preparing to only expose instances of struct ctl_table
as "const".  This will also affect the ctl_table argument of sysctl
handlers.

As the function prototype of all sysctl handlers throughout the tree
needs to stay consistent that change will be done in one commit.

To reduce the size of that final commit, switch utility functions which
are not bound by "typedef proc_handler" to "const struct ctl_table".

No functional change.

Link: https://lkml.kernel.org/r/20240518-sysctl-const-handler-hugetlb-v1-1-47e34e2871b2@weissschuh.net
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: Joel Granados <j.granados@samsung.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>