iio: adc: Fix incorrect exit of for-loop

iio: adc: Fix incorrect exit of for-loop

Currently the for-loop that scans for the optimial adc_period iterates
through all the possible adc_period levels because the exit logic in
the loop is inverted. I believe the comparison should be swapped and
the continue replaced with a break to exit the loop at the correct
point.

Addresses-Coverity: ("Continue has no effect")
Fixes: e08e19c331fb ("iio:adc: add iio driver for Palmas (twl6035/7) gpadc")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210730071651.17394-1-colin.king@canonical.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>