staging:iio:dac:ad5446: Remove duplicated chip_info entries

There are three identical chip_info entries. Remove two of them and use the id
of the remaining entry for all three device table entries.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>