Staging: iio: ad7816: constify attribute_group structures

Check for attribute_group structures that are only stored in the
event_attrs filed of iio_info structure. As the event_attrs field
of iio_info structures is constant, so these attribute_group
structures can also be declared constant.
Done using coccinelle:

@r1 disable optional_qualifier @
identifier i;
position p;
@@
static struct attribute_group i@p = {...};

@ok1@
identifier r1.i;
position p;
struct iio_info x;
@@
x.event_attrs=&i@p;

@bad@
position p!={r1.p,ok1.p};
identifier r1.i;
@@
i@p

@depends on !bad disable optional_qualifier@
identifier r1.i;
@@
static
+const
struct attribute_group i={...};

@depends on !bad disable optional_qualifier@
identifier r1.i;
@@
+const
struct attribute_group i;

File size before:
text data bss dec hex filename
3295 768 0 4063 fdf drivers/staging/iio/adc/ad7816.o

File size after:
text data bss dec hex filename
3359 736 0 4095 fff drivers/staging/iio/adc/ad7816.o

Signed-off-by: Bhumika Goyal <[e-mail]>
Acked-by: Julia Lawall <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/staging/iio/adc/ad7816.c

···
 	NULL,
 };
 
-static struct attribute_group ad7816_event_attribute_group = {
+static const struct attribute_group ad7816_event_attribute_group = {
 	.attrs = ad7816_event_attributes,
 	.name = "events",
 };