iio: adc: adi-axi-adc: improve probe() error messaging

iio: adc: adi-axi-adc: improve probe() error messaging

The current error handling for calls such as devm_clk_get_enabled() in
the adi-axi-adc probe() function means that, if a property such as
'clocks' (for example) is not present in the devicetree when booting a
kernel with the driver enabled, the resulting error message will be
vague, e.g.:

|adi_axi_adc 44a00000.backend: probe with driver adi_axi_adc failed with error -2

Change the devm_clk_get_enabled(), devm_regmap_init_mmio(), and
devm_iio_backend_register() checks to use dev_err_probe() with some
context for easier debugging.

After the change:

|adi_axi_adc 44a00000.backend: error -ENOENT: failed to get clock
|adi_axi_adc 44a00000.backend: probe with driver adi_axi_adc failed with error -2

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240613163407.2147884-1-tgamblin@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>