spi: spi-fsl-dspi: Make bus-num property optional

- pinctrl-0: pin control group to be used for this controller.

- pinctrl-names: must contain a "default" entry.

- spi-num-chipselects : the number of the chipselect signals.

- bus-num : the slave chip chipselect signal number.

Optional property:

- big-endian: If present the dspi device's registers are implemented

  in big endian mode.

- bus-num : the slave chip chipselect signal number.

Optional SPI slave node properties:

- fsl,spi-cs-sck-delay: a delay in nanoseconds between activating chip

	const struct regmap_config *regmap_config;

	struct fsl_dspi_platform_data *pdata;

	struct spi_controller *ctlr;

	int ret, cs_num, bus_num;

	int ret, cs_num, bus_num = -1;

	struct fsl_dspi *dspi;

	struct resource *res;

	void __iomem *base;

		}

		ctlr->num_chipselect = cs_num;

		ret = of_property_read_u32(np, "bus-num", &bus_num);

		if (ret < 0) {

			dev_err(&pdev->dev, "can't get bus-num\n");

			goto out_ctlr_put;

		}

		of_property_read_u32(np, "bus-num", &bus_num);

		ctlr->bus_num = bus_num;

		if (of_property_read_bool(np, "spi-slave"))