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

Commit 9e61d901 ("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 388be488 ("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.jpSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/tsl2563.c

@@ -803,12 +803,11 @@ static int tsl2563_remove(struct i2c_client *client)
 
 	iio_device_unregister(indio_dev);
 	if (!chip->int_enabled)
-		cancel_delayed_work(&chip->poweroff_work);
+		cancel_delayed_work_sync(&chip->poweroff_work);
 	/* Ensure that interrupts are disabled - then flush any bottom halves */
 	chip->intr &= ~0x30;
 	i2c_smbus_write_byte_data(chip->client, TSL2563_CMD | TSL2563_REG_INT,
 				  chip->intr);
-	flush_scheduled_work();
 	tsl2563_set_power(chip, 0);
 
 	return 0;