iopoll: update kerneldoc of read_poll_timeout_atomic()

Arguments description of read_poll_timeout_atomic() is out of date,
update it.

Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1600668815-12135-11-git-send-email-chunfeng.yun@mediatek.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>