iio: adc: mp2629: Drop duplicate setting iio_dev.dev.parent

This is already set to the same value in devm_iio_device_alloc()

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Saravanan Sekar <sravanhome@gmail.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210426170251.351957-4-jic23@kernel.org