iio: light: tsl2563: Replace flush_scheduled_work() with cancel_delayed_work_sync().

iio: light: tsl2563: Replace flush_scheduled_work() with cancel_delayed_work_sync().

Commit 36e3ab1e9cfe09aa ("iio: light: tsl2563: Remove
flush_scheduled_work") replaced cancel_delayed_work() +
flush_scheduled_work() with cancel_delayed_work_sync() for only
tsl2563_probe() side.

Do the same thing for tsl2563_remove() side, which was added by
commit f0558a76ac77a8cd ("staging:iio: tsl2563 abi fixes and interrupt
handling").

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/3381176e-2f86-24ba-a8ba-c4ce8f416086@I-love.SAKURA.ne.jp
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>