iio: dac: ad5446: Don't set error code to voltage_uv
iio: dac: ad5446: Don't set error code to voltage_uv

regulator_get_voltage() may return negative error code.
Add error checking to avoid setting error code to voltage_uv.

Signed-off-by: Axel Lin <b6ffd6973e972cb999e8e535ab74da7fee0c035f@ingics.com>
Signed-off-by: Jonathan Cameron <09f65b71b7655725897b2fd41a09a0cefe2e1ace@kernel.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs