This patch allows the lp5521 driver to be successfully probed and
initialised when Device Tree support is enabled.

Based on a patch by Gabriel Fernandez, rewritten in accordance
with review feedback.

Cc: Gabriel Fernandez <gabriel.fernandez@stericsson.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Acked-by: NMilo Kim <milo.kim@ti.com>
Signed-off-by: NBryan Wu <cooloney@gmail.com>