iio: adc: twl4030: Use false / true instead of 0 / 1 with booleans

Suggestion from coccinelle / coccicheck

CHECK   drivers/iio/adc/twl4030-madc.c
drivers/iio/adc/twl4030-madc.c:524:6-15: WARNING: Comparison of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:655:1-43: WARNING: Assignment of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:659:2-44: WARNING: Assignment of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:664:1-43: WARNING: Assignment of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:498:2-34: WARNING: Assignment of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:510:2-19: WARNING: Assignment of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:511:2-11: WARNING: Assignment of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:531:2-19: WARNING: Assignment of 0/1 to bool variable
drivers/iio/adc/twl4030-madc.c:532:2-11: WARNING: Assignment of 0/1 to bool variable

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Sebastian Reichel <sre@kernel.org>