spi: rockchip-sfc: Fix double-free in remove() callback

In the Linux kernel, the following vulnerability has been resolved:

spi: rockchip-sfc: Fix double-free in remove() callback

The driver uses devm_spi_register_controller() for registration, which

automatically unregisters the controller via devm cleanup when the

device is removed. The manual call to spi_unregister_controller() in

the remove() callback can lead to a double-free.

And to make sure controller is unregistered before DMA buffer is

unmapped, switch to use spi_register_controller() in probe().