perf/imx_ddr: Constify static struct attribute_group

The only usage is to put their addresses in an array of pointers to
const struct attribute group. Make them const to allow the compiler
to put them in read-only memory.

Signed-off-by: Rikard Falkeborn <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

drivers/perf/fsl_imx8_ddr_perf.c

···
 	NULL,
 };
 
-static struct attribute_group ddr_perf_identifier_attr_group = {
+static const struct attribute_group ddr_perf_identifier_attr_group = {
 	.attrs = ddr_perf_identifier_attrs,
 	.is_visible = ddr_perf_identifier_attr_visible,
 };
···
 	NULL,
 };
 
-static struct attribute_group ddr_perf_filter_cap_attr_group = {
+static const struct attribute_group ddr_perf_filter_cap_attr_group = {
 	.name = "caps",
 	.attrs = ddr_perf_filter_cap_attr,
 };
···
 	NULL,
 };
 
-static struct attribute_group ddr_perf_cpumask_attr_group = {
+static const struct attribute_group ddr_perf_cpumask_attr_group = {
 	.attrs = ddr_perf_cpumask_attrs,
 };
 
···
 	NULL,
 };
 
-static struct attribute_group ddr_perf_events_attr_group = {
+static const struct attribute_group ddr_perf_events_attr_group = {
 	.name = "events",
 	.attrs = ddr_perf_events_attrs,
 };
···
 	NULL,
 };
 
-static struct attribute_group ddr_perf_format_attr_group = {
+static const struct attribute_group ddr_perf_format_attr_group = {
 	.name = "format",
 	.attrs = ddr_perf_format_attrs,
 };