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 <bhumirks@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/ad7816.c

@@ -327,7 +327,7 @@ static struct attribute *ad7816_event_attributes[] = {
 	NULL,
 };
 
-static struct attribute_group ad7816_event_attribute_group = {
+static const struct attribute_group ad7816_event_attribute_group = {
 	.attrs = ad7816_event_attributes,
 	.name = "events",
 };