power_supply: 88pm860x: Fix leaked power supply on probe fail

Driver forgot to unregister power supply if request_threaded_irq()
failed in probe(). In such case the memory associated with power supply
leaked.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Fixes: a830d28b ("power_supply: Enable battery-charger for 88pm860x")
Cc: <stable@vger.kernel.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>