iio: adc: ad7768-1: Move setting of val a bit later to avoid unnecessary return value check

The data used is all in local variables so there is no advantage
in setting *val = ret with the direct mode claim held.
Move it later to after error check.

Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250217141630.897334-13-jic23@kernel.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>