iio: adc: ad4030: check scan_type for error

iio: adc: ad4030: check scan_type for error

Check scan_type for error ad4030_get_chan_scale(). Currently, this
should never fail, but it is good practice to always check for errors
in case of future changes.

Calling iio_get_current_scan_type() is moved out of the if statement
also to avoid potential issues with future changes instead of assuming
that the non-differential case does not use extended scan_type.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202503040954.n6MhjSsV-lkp@intel.com/
Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250310-iio-adc-ad4030-check-scan-type-err-v1-1-589e4ebd9711@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>