staging: iio: ad9834: use dev_err_probe() in probe function

staging: iio: ad9834: use dev_err_probe() in probe function

Replace open-coded dev_err() + return sequences with dev_err_probe(),
which is the preferred pattern for probe error paths as it handles
deferred probing correctly and reduces boilerplate.

Convert all three remaining instances in ad9834_probe():
 - master clock enable failure
 - device init SPI sync failure

The avdd regulator path already used dev_err_probe().

Signed-off-by: Angus Gardner <angusg778@gmail.com>
Reviewed-by: Maxwell Doose <m32285159@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>