drivers/xen: use helper macro __ATTR_RW

Use helper macro __ATTR_RW to define HYPERVISOR_ATTR_RW to make code more clear.
Minor readability improvement.

Remove extra whitespace [boris: added this comment]
Signed-off-by: zhanglianjie <zhanglianjie@uniontech.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20220305133823.158961-1-zhanglianjie@uniontech.comSigned-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/sys-hypervisor.c

@@ -25,8 +25,7 @@
 static struct hyp_sysfs_attr _name##_attr = __ATTR_RO(_name)
 
 #define HYPERVISOR_ATTR_RW(_name) \
-static struct hyp_sysfs_attr _name##_attr = \
-	__ATTR(_name, 0644, _name##_show, _name##_store)
+static struct hyp_sysfs_attr _name##_attr = __ATTR_RW(_name)
 
 struct hyp_sysfs_attr {
 	struct attribute attr;