intel_th: Constify attribute_group structs

The only usage of them is to pass their address to sysfs_create_group()
and sysfs_remove_group(), both which have pointers to const
attribute_group structs as input. Make them const to allow the compiler
to put them in read-only memory.

Signed-off-by: Rikard Falkeborn <[e-mail]>
Signed-off-by: Alexander Shishkin <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/hwtracing/intel_th/intel_th.h

···
 	/* file_operations for those who want a device node */
 	const struct file_operations *fops;
 	/* optional attributes */
-	struct attribute_group	*attr_group;
+	const struct attribute_group *attr_group;
 
 	/* source ops */
 	int			(*set_output)(struct intel_th_device *thdev,

drivers/hwtracing/intel_th/msu.c

···
 	NULL,
 };
 
-static struct attribute_group msc_output_group = {
+static const struct attribute_group msc_output_group = {
 	.attrs	= msc_output_attrs,
 };
 

drivers/hwtracing/intel_th/pti.c

···
 	NULL,
 };
 
-static struct attribute_group pti_output_group = {
+static const struct attribute_group pti_output_group = {
 	.attrs	= pti_output_attrs,
 };
 
···
 	NULL,
 };
 
-static struct attribute_group lpp_output_group = {
+static const struct attribute_group lpp_output_group = {
 	.attrs	= lpp_output_attrs,
 };