xen: constify all instances of "struct attribute_group"

The functions these get passed to have been taking pointers to const
since at least 2.6.16.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

---
 drivers/xen/sys-hypervisor.c  |    6 +++---
 drivers/xen/xen-balloon.c     |    2 +-
 drivers/xen/xen-selfballoon.c |    2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

--- 3.3-rc4/drivers/xen/sys-hypervisor.c
+++ 3.3-rc4-xen-const-attribute_group/drivers/xen/sys-hypervisor.c
@@ -97,7 +97,7 @@ static struct attribute *version_attrs[]
 	NULL
 };
 
-static struct attribute_group version_group = {
+static const struct attribute_group version_group = {
 	.name = "version",
 	.attrs = version_attrs,
 };
@@ -210,7 +210,7 @@ static struct attribute *xen_compile_att
 	NULL
 };
 
-static struct attribute_group xen_compilation_group = {
+static const struct attribute_group xen_compilation_group = {
 	.name = "compilation",
 	.attrs = xen_compile_attrs,
 };
@@ -340,7 +340,7 @@ static struct attribute *xen_properties_
 	NULL
 };
 
-static struct attribute_group xen_properties_group = {
+static const struct attribute_group xen_properties_group = {
 	.name = "properties",
 	.attrs = xen_properties_attrs,
 };
--- 3.3-rc4/drivers/xen/xen-balloon.c
+++ 3.3-rc4-xen-const-attribute_group/drivers/xen/xen-balloon.c
@@ -207,7 +207,7 @@ static struct attribute *balloon_info_at
 	NULL
 };
 
-static struct attribute_group balloon_info_group = {
+static const struct attribute_group balloon_info_group = {
 	.name = "info",
 	.attrs = balloon_info_attrs
 };
--- 3.3-rc4/drivers/xen/xen-selfballoon.c
+++ 3.3-rc4-xen-const-attribute_group/drivers/xen/xen-selfballoon.c
@@ -488,7 +488,7 @@ static struct attribute *selfballoon_att
 	NULL
 };
 
-static struct attribute_group selfballoon_group = {
+static const struct attribute_group selfballoon_group = {
 	.name = "selfballoon",
 	.attrs = selfballoon_attrs
 };