ASoC: dt-bindings: tlv320adc3xxx: Fix incorrect GPIO description

Fix the description for the ti,dmdin-gpio1 and ti,dmclk-gpio2
properties to correctly describe that when configured as general
purpose outputs (ADC3XXX_GPIO_GPO), the pins are available via
the GPIO framework.

Signed-off-by: Ricard Wanderlof <ricard.wanderlof@axis.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://msgid.link/r/20240528-tlv320adc3xxx-dt-gpio-fix-v1-1-209fb2c2f86f@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>