spi: bcm2835: Drop assignment of dma_slave_config direction

spi: bcm2835: Drop assignment of dma_slave_config direction

The BCM2835 SPI driver still sets the "direction" member in struct
dma_slave_config even though it was deprecated five years ago with
commit d9ff958bb34a ("dmaengine: Mark the struct dma_slave_config
direction field deprecated") and is no longer evaluated by the BCM2835
DMA driver since commit 00648f4d0f41 ("dmaengine: bcm2835: remove
dma_slave_config direction usage").

Drop the superfluous assignment.
No functional change intended.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Frank Pavlic <f.pavlic@kunbus.de>
Cc: Martin Sperl <kernel@martin.sperl.org>
Cc: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>