twl4030_charger: convert to module_platform_driver instead of ..._probe.

Drivers using module_platform_driver_probe cannot return
EPROBE_DEFER from the probe function, which makes them rather useless
these days...

Convert to module_platform_driver() so EPROBE_DEFER can be used.

Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Sebastian Reichel <sre@kernel.org>