spi: dln2: Pass of_node to spi master

This allows defining SPI devices connected to a DLN2 using devicetree.

This already works for i2c because of a similar patch:
3b10db23

: i2c: dln2: set the device tree node of the adapter

Signed-off-by: Crestez Dan Leonard <leonard.crestez@intel.com>
Acked-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>