sunxi-rsb: Include OF based modalias in device uevent

Include the OF-based modalias in the uevent sent when registering devices
on the sunxi RSB bus, so that user space has a chance to autoload the
kernel module for the device.

Fixes a regression caused by commit 3f241bfa ("arm64: allwinner: a64:
pine64: Use dcdc1 regulator for mmc0"). When the axp20x-rsb module for
the AXP803 PMIC is built as a module, it is not loaded and the system
ends up with an disfunctional MMC controller.

Fixes: d787dcdb ("bus: sunxi-rsb: Add driver for Allwinner Reduced Serial Bus")
Cc: stable <stable@vger.kernel.org> # 4.4.x 7a3b7cd3 of: device: Export of_device_{get_modalias, uvent_modalias} to modules
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>