leds: 88pm860x - fix checking in probe function

Improve device and platform data checks in probe function.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>