spi: pic32: stop setting dma_config->slave_id

Setting slave_id makes no sense with DT based probing, and
should eventually get removed entirely. Address this driver
by no longer setting the field here.

I could not find which DMA driver is used on PIC32, if it's
in the tree at all, but none of the obvious ones even care
about slave_id any more.

Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20211122222203.4103644-4-arnd@kernel.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>