max17042_battery: Fix power supply and irq registration ordering

IRQ registration should happen only after power supply object usable.
This patch fixes the ordering of power supply and irq registration
calls.

Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>