The comparator polarity field in config register is not correctly
initialized as per the interrupt trigger setting.  Because the bitfield
definision is wrong and bit shifting is missed.

Fixes: d9f39bab ("iio: adc: ti-ads1015: add threshold event support")
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>