leds: lp50xx: Switch to new style i2c-driver probe function

Switch to the new style i2c-driver probe_new probe function.
Note we do not have any old style board files using this but
user still has a possibility to instantiate device from sysfs.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>