On unbind of the BCM2835 SPI driver, the SPI controller is disabled
first and the DMA channels are terminated and torn down afterwards.

This seems backwards:  In the theoretical case that DMA is active,
it might try to fill the SPI FIFOs even after the controller has
been disabled.

Reverse the order, thereby mirroring what's done on ->probe().
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/ac79f1e3d6fd9a1f5e0cb4008c43b98ea70be3c2.1589557526.git.lukas@wunner.deSigned-off-by: Mark Brown <broonie@kernel.org>