iio: adc: ti_am335x_adc: Fix return value check of tiadc_request_dma()

Fix wrong handling of a DMA request where the probing only failed
if -EPROPE_DEFER was returned. Instead, let us fail if a non -ENODEV
value is returned. This makes DMAs explicitly optional. Even if the
DMA request is unsuccessfully, the ADC can still work properly.
We do also handle the defer probe case by making use of dev_err_probe().

Fixes: f438b9da

 ("drivers: iio: ti_am335x_adc: add dma support")
Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Reviewed-by: Bhavya Kapoor <b-kapoor@ti.com>
Link: https://lore.kernel.org/r/20230925134427.214556-1-w.egorov@phytec.de


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>