leds: lm3533: constify attribute_group structure

Functions working with attribute_groups provided by <linux/device.h>
work with const attribute_group. These attribute_group structures do not
change at runtime so mark them as const.

File size before:
 text      data     bss     dec     hex filename
 8272      4608      64   12944    3290 drivers/leds/leds-lm3533.o

File size after:
 text      data     bss     dec     hex filename
 8368      4512      64   12944    3290 drivers/leds/leds-lm3533.o

This change was made with the help of Coccinelle.

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>