staging:iio:adc:MXS:LRADC: fix touchscreen statemachine

Releasing the touchscreen lets the internal statemachine left in a wrong state.
Due to this the release coordinate will be reported again by accident when the next
touchscreen event happens. This change sets up the correct state when waiting
for the next touchscreen event.

This has led to reported issues with calibrating the touchscreen.
Bug was introduced somewhere in the series that began with
18da755d
Staging/iio/adc/touchscreen/MXS: add proper clock handling
in which the way this driver worked was substantially changed
to be interrupt driven rather than relying on a busy loop.
This was a regression in the 3.13 kernel.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
Tested-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>