power: supply: bq27xxx_battery: Silence deferred-probe error

The driver fails to probe with -EPROBE_DEFER if battery's power supply
(charger driver) isn't ready yet and this results in a bit noisy error
message in KMSG during kernel's boot up. Let's silence the harmless
error message.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>