samples/kobject: make attribute_group const

The attr_group structures are allocated once and never modified at
runtime.  Also to match the const‑qualified parameter of
sysfs_create_group().

Signed-off-by: Meng Shao Liu <sau525@gmail.com>
Link: https://lore.kernel.org/r/dc94227eaf337a2b92ab77dffa0da9f7f1f84c4e.1752646650.git.sau525@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>