mm: shmem: use helper macro __ATTR_RW

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

Link: https://lkml.kernel.org/r/20220312082252.55586-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shmem.c

@@ -3965,8 +3965,7 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
 	return count;
 }
 
-struct kobj_attribute shmem_enabled_attr =
-	__ATTR(shmem_enabled, 0644, shmem_enabled_show, shmem_enabled_store);
+struct kobj_attribute shmem_enabled_attr = __ATTR_RW(shmem_enabled);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_SYSFS */
 
 #else /* !CONFIG_SHMEM */