iio: adc: ti-ads1119: Reinit completion before wait_for_completion_timeout()

iio: adc: ti-ads1119: Reinit completion before wait_for_completion_timeout()

The completion is not reinit before wait_for_completion_timeout(),
so wait_for_completion_timeout() will return immediately after
the first successful completion.

Fixes: a9306887eba4 ("iio: adc: ti-ads1119: Add driver")
Signed-off-by: Felix Gu <ustc.gu@gmail.com>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>