ACPI / dock: constify attribute_group structure

Functions working with attribute_groups provided by <linux/sysfs.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
 7902      3528      64   11494    2ce6 drivers/acpi/dock.o

File size after:
 text      data     bss     dec     hex filename
 7998      3432      64   11494    2ce6 drivers/acpi/dock.o

This change was made with the help of Coccinelle.
Signed-off-by: NAmitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/dock.c

@@ -585,7 +585,7 @@ static struct attribute *dock_attributes[] = {
 	NULL
 };
 
-static struct attribute_group dock_attribute_group = {
+static const struct attribute_group dock_attribute_group = {
 	.attrs = dock_attributes
 };