iio: adc: ti-ads124s08: Return reset GPIO lookup errors

iio: adc: ti-ads124s08: Return reset GPIO lookup errors

devm_gpiod_get_optional() returns NULL when the optional GPIO is absent,
but returns an ERR_PTR when the GPIO provider lookup fails, including
probe deferral.

Probe currently logs the ERR_PTR case as if the reset GPIO were simply
absent and keeps the error pointer in reset_gpio. Later ads124s_reset()
treats any non-NULL reset_gpio as a valid descriptor and passes it to
gpiod_set_value_cansleep().

Return the lookup error instead of retaining the ERR_PTR.

Fixes: e717f8c6dfec ("iio: adc: Add the TI ads124s08 ADC code")
Cc: stable@vger.kernel.org
Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>