iio: adc: ti-ads131e08: Drop duplicate setting of iio_dev.dev.parent

Already set to same value in devm_iio_device_alloc()

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Tomislav Denis <tomislav.denis@avl.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210426170251.351957-6-jic23@kernel.org