staging: most: configfs: Make mdev_link_list static

Fix sparse warning:

drivers/staging/most/configfs.c:34:18: warning:
 symbol 'mdev_link_list' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/configfs.c

@@ -31,7 +31,7 @@ struct mdev_link {
 	char comp_params[PAGE_SIZE];
 };
 
-struct list_head mdev_link_list;
+static struct list_head mdev_link_list;
 
 static int set_cfg_buffer_size(struct mdev_link *link)
 {