drivers: led: lp5569: enable auto-increment

The lp5569 controller supports auto-increment for its registers. This is by
default enabled in the chip, but the driver actively disabled it.

Since auto-increment is useful for writing multiple consecutive registers,
enable the feature. The driver, however, doesn't perform such consecutive
writes and thus the existing behavior is not altered.

Signed-off-by: Emil Dahl Juhl <emdj@bang-olufsen.dk>