iio: dac: ds4422/ds4424 drop of_node check

commit a2d2010d95cd7ffe3773aba6eaee35d54e332c25 upstream.

The driver doesn't actually rely on any DT properties. Removing this
check makes it usable on ACPI based platforms.

Signed-off-by: Ruslan Babayev <ruslan@babayev.com>
Cc: xe-linux-external@cisco.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>