power: supply: s3c_adc_battery: fix possible use-after-free in s3c_adc_bat_remove()

[ Upstream commit 68ae256945d2abe9036a7b68af4cc65aff79d5b7 ]

This driver's remove path calls cancel_delayed_work(). However, that
function does not wait until the work function finishes. This means
that the callback function may still be running after the driver's
remove function has finished, which would result in a use-after-free.

Fix by calling cancel_delayed_work_sync(), which ensures that
the work is properly cancelled, no longer running, and unable
to re-schedule itself.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>