power: supply: max14656: fix potential use-before-alloc

Call order on probe():
- max14656_hw_init() enables interrupts on the chip
- devm_request_irq() starts processing interrupts, isr
  could be called immediately
-    isr: schedules delayed work (irq_work)
-    irq_work: calls power_supply_changed()
- devm_power_supply_register() registers the power supply

Depending on timing, it's possible that power_supply_changed()
is called on an unregistered power supply structure.

Fix by registering the power supply before requesting the irq.

Cc: Alexander Kurz <akurz@blala.de>
Signed-off-by: Sven Van Asbroeck <TheSven73@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>