iio: adc: rockchip_saradc: reset saradc controller before programming it

iio: adc: rockchip_saradc: reset saradc controller before programming it

BugLink: http://bugs.launchpad.net/bugs/1627730
commit 543852af8e5902aee8f7c72c89e1513663e0f696 upstream.

SARADC controller needs to be reset before programming it, otherwise
it will not function properly.

Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-iio@vger.kernel.org
Cc: linux-rockchip@lists.infradead.org
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>