power_supply: Don't iterate over devices to return -EPROBE_DEFER

This piece of code was added so that we return -EPROBE_DEFER when no devices are
registered. But even if class_for_each_device() returns 0, we are going to
return -EPROBE_DEFER only.

And so this code isn't required at all. Remove it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>