power: supply: da9150: Fix use after free bug in da9150_charger_remove due to race condition

In da9150_charger_probe, &charger->otg_work is bound with
da9150_charger_otg_work. da9150_charger_otg_ncb may be
called to start the work.

If we remove the module which will call da9150_charger_remove
to make cleanup, there may be a unfinished work. The possible
sequence is as follows:

Fix it by canceling the work before cleanup in the da9150_charger_remove

CPU0                  CPUc1

                    |da9150_charger_otg_work
da9150_charger_remove      |
power_supply_unregister  |
device_unregister   |
power_supply_dev_release|
kfree(psy)          |
                    |
                    | 	power_supply_changed(charger->usb);
                    |   //use

Fixes: c1a281e3 ("power: Add support for DA9150 Charger")
Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>