iio: dac: ltc2632 remove redundant pointer chip_info and spi_dev_id

Pointers chip_info and spi_dev_id are being assigned but are never used
hence they are redundant and can be removed.

Cleans up clang warning:
warning: variable 'chip_info' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>