iio: adc: mt6360: Drop duplicate setting of iio_dev.dev.parent

Already set to the same value in devm_iio_device_alloc()

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Gene Chen <gene_chen@richtek.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210426170251.351957-5-jic23@kernel.org