gpio-charger: Fix potential race between irq handler and probe/remove

This patch fixes a potential race between the irq handler and the probe
and remove functions.

The irq should not be requested before the chargers power_supply has been
registered and has to be freed before the power_supply is unregistered,
otherwise it is possible that the irq fires while the power_supply is not
initialized yet or has already been freed.

While we are at it replace request_irq with request_any_context_irq.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>