Staging: iio: adc: constify attribute_group structures

Check for attribute_group structures that are only stored in the
attrs filed of iio_info structure. As the 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.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: drivers/staging/iio/adc/ad7280a.o
   text	   data	    bss	    dec	    hex	filename
   6487	    584	    776	   7847	   1ea7
drivers/staging/iio/adc/ad7280a.o

File size after: drivers/staging/iio/adc/ad7280a.o
   text	   data	    bss	    dec	    hex	filename
   6551	    544	    776	   7871	   1ebf
drivers/staging/iio/adc/ad7280a.o
Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/adc/ad7280a.c

@@ -478,7 +478,7 @@ static ssize_t ad7280_store_balance_timer(struct device *dev,
 static struct attribute *ad7280_attributes[AD7280A_MAX_CHAIN *
 					   AD7280A_CELLS_PER_DEV * 2 + 1];
 
-static struct attribute_group ad7280_attrs_group = {
+static const struct attribute_group ad7280_attrs_group = {
 	.attrs = ad7280_attributes,
 };