staging: iio: ad5933: fix order of cycle conditions

Correctly handle the settling time cycles value. The else branch is an
impossible condition, > 1022 in the else branch of > 511. Flipping the order.

Based on the Table 13 at the bottom of Page 25 of the Data Sheet:
http://www.analog.com/media/en/technical-documentation/data-sheets/AD5933.pdf



Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>