atm: uapi: fix spelling typos in comments

Fix the typo of 'Unsuported' in atmbr2684.h

Signed-off-by: Rong Tao <rongtao@cestc.cn>
Link: https://lore.kernel.org/r/tencent_F1354BEC925C65EA357E741E91DF2044E805@qq.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>