iio: adc: adi-axi-adc: Fix object reference counting

When looking for a registered client to attach with, the wrong reference
counters are being grabbed. The idea is to increment the module and device
counters of the client device and not the counters of the axi device being
probed.

Fixes: ef040706 (iio: adc: adi-axi-adc: add support for AXI ADC IP core)

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Acked-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>