power: supply: bd70528: Add MODULE_ALIAS to allow module auto loading

The bd70528 charger driver is probed by MFD driver. Add MODULE_ALIAS
in order to allow udev to load the module when MFD sub-device cell for
charger is added.

Fixes: f8c7f7dd ("power: supply: Initial support for ROHM BD70528 PMIC charger block")
Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>