nvme: constify static attribute_group structs

The only usage of these is to put their addresses in arrays of pointers
to const attribute_groups. Make them const to allow the compiler to put
them in read-only memory.
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -2859,7 +2859,7 @@ static struct attribute *nvme_subsys_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group nvme_subsys_attrs_group = {
+static const struct attribute_group nvme_subsys_attrs_group = {
 	.attrs = nvme_subsys_attrs,
 };
 
@@ -3694,7 +3694,7 @@ static umode_t nvme_dev_attrs_are_visible(struct kobject *kobj,
 	return a->mode;
 }
 
-static struct attribute_group nvme_dev_attrs_group = {
+static const struct attribute_group nvme_dev_attrs_group = {
 	.attrs		= nvme_dev_attrs,
 	.is_visible	= nvme_dev_attrs_are_visible,
 };

drivers/nvme/host/fc.c

@@ -3789,7 +3789,7 @@ static struct attribute *nvme_fc_attrs[] = {
 	NULL
 };
 
-static struct attribute_group nvme_fc_attr_group = {
+static const struct attribute_group nvme_fc_attr_group = {
 	.attrs = nvme_fc_attrs,
 };
 

drivers/nvme/target/fcloop.c

@@ -1545,7 +1545,7 @@ static struct attribute *fcloop_dev_attrs[] = {
 	NULL
 };
 
-static struct attribute_group fclopp_dev_attrs_group = {
+static const struct attribute_group fclopp_dev_attrs_group = {
 	.attrs		= fcloop_dev_attrs,
 };