iio: adc: cpcap: Remove hung interrupt quirk

This is no longer needed as the real problem was interrupt flags
not getting passed properly from device tree to the cpcap-core.c
mfd driver. This got fixed with commit ac894732 ("mfd: cpcap:
Fix interrupt to use level interrupt") So let's remove ADC
interrupt specific the quirk.

Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>