bus: sunxi-rsb: Fix error handling in sunxi_rsb_init()

The sunxi_rsb_init() returns the platform_driver_register() directly
without checking its return value, if platform_driver_register() failed,
the sunxi_rsb_bus is not unregistered.
Fix by unregister sunxi_rsb_bus when platform_driver_register() failed.

Fixes: d787dcdb

 ("bus: sunxi-rsb: Add driver for Allwinner Reduced Serial Bus")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20221123094200.12036-1-yuancan@huawei.com
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>