const_structs.checkpatch: add ctl_table

Now that the sysctl core can handle "const struct ctl_table", make
sure that new usages of the struct already enter the tree as const.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Joel Granados <joel.granados@kernel.org>

Author: t-8ch

scripts/const_structs.checkpatch

@@ -6,6 +6,7 @@ bus_type
 clk_ops
 comedi_lrange
 component_ops
+ctl_table
 dentry_operations
 dev_pm_ops
 device_type