regulator: da9052: fix bug in device tree iteration loop

The driver of da9052 is buggy due to the iteration loop of device tree.
This patch fix the loop condition to make the driver work with device tree.

Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>