mfd: twl4030-madc: Cleanup driver

Some style fixes in twl4030-madc driver.

Reported-by: Jonathan Cameron <jic23@kernel.org>
Reported-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Sebastian Reichel <sre@debian.org>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Tested-by: Marek Belisko <marek@goldelico.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>