power: max17040: Fix NULL pointer dereference when there is no platform_data

Fix NULL pointer dereference of "chip->pdata" if platform_data was not
supplied to the driver.

The driver during probe stored the pointer to the platform_data:
	chip->pdata = client->dev.platform_data;
Later it was dereferenced in max17040_get_online() and
max17040_get_status().

If platform_data was not supplied, the NULL pointer exception would
happen:

[    6.626094] Unable to handle kernel  of a at virtual address 00000000
[    6.628557] pgd = c0004000
[    6.632868] [00000000] *pgd=66262564
[    6.634636] Unable to handle kernel paging request at virtual address e6262000
[    6.642014] pgd = de468000
[    6.644700] [e6262000] *pgd=00000000
[    6.648265] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
[    6.653552] Modules linked in:
[    6.656598] CPU: 0 PID: 31 Comm: kworker/0:1 Not tainted 3.10.14-02717-gc58b4b4 #505
[    6.664334] Workqueue: events max17040_work
[    6.668488] task: dfa11b80 ti: df9f6000 task.ti: df9f6000...