arcnet: com20020-pci: constify attribute_group structures.

attribute_group are not supposed to change at runtime. All functions
working with attribute_group provided by <linux/netdevice.h> work
with const attribute_group. So mark the non-const structs as const.

File size before:
text data bss dec hex filename
3409 948 28 4385 1121 drivers/net/arcnet/com20020-pci.o

File size After adding 'const':
text data bss dec hex filename
3473 884 28 4385 1121 drivers/net/arcnet/com20020-pci.o

Signed-off-by: Arvind Yadav <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/arcnet/com20020-pci.c

···
 	NULL,
 };
 
-static struct attribute_group com20020_state_group = {
+static const struct attribute_group com20020_state_group = {
 	.name = NULL,
 	.attrs = com20020_state_attrs,
 };