usb: phy-tahvo: constify attribute_group structures.

attribute_group are not supposed to change at runtime. All functions
working with attribute_group provided by <linux/sysfs.h> work with
const attribute_group. So mark the non-const structs as const.
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/phy/phy-tahvo.c

@@ -326,7 +326,7 @@ static struct attribute *tahvo_attributes[] = {
 	NULL
 };
 
-static struct attribute_group tahvo_attr_group = {
+static const struct attribute_group tahvo_attr_group = {
 	.attrs = tahvo_attributes,
 };