power_supply: tps65217-charger: Fix NULL deref during property export

This bug leads to:

[    1.906411] Unable to handle kernel NULL pointer dereference at virtual address 0000000c
[    1.914878] pgd = c0004000
[    1.917786] [0000000c] *pgd=00000000
[    1.921536] Internal error: Oops: 5 [#1] SMP ARM
[    1.926357] Modules linked in:
[    1.929556] CPU: 0 PID: 14 Comm: kworker/0:1 Not tainted 4.4.5 #18
[    1.936006] Hardware name: Generic AM33XX (Flattened Device Tree)
[    1.942383] Workqueue: events power_supply_changed_work
[    1.947842] task: de2c41c0 ti: de2c8000 task.ti: de2c8000
[    1.953483] PC is at tps65217_ac_get_property+0x14/0x28
[    1.958937] LR is at tps65217_ac_get_property+0x10/0x28

Driver was trying to use drv_data in property get handler. However drv_data
was not set, so it caused NULL pointer dereference. This patch properly
sets drv_data during probe by power_supply_config parameter, so the
property get handler works as desired.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Fixes: 3636859b280c ("power_supply: Add support for tps65217-charger")
Signed-off-by: Sebastian Reichel <sre@kernel.org>