iio: remove gpio interrupt probing from drivers that use a single interrupt

Commit 845c8770 ("i2c / ACPI: Assign IRQ for devices that have
GpioInt automatically") automatically assigns the first ACPI GPIO
interrupt in client->irq, so we can remove the probing code from
drivers that use only one interrupt.

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>