spi: fsl-dspi: Make of_device_id array const

Make of_device_id array const, because all OF functions
handle it as const.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-fsl-dspi.c

@@ -406,7 +406,7 @@ static irqreturn_t dspi_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
-static struct of_device_id fsl_dspi_dt_ids[] = {
+static const struct of_device_id fsl_dspi_dt_ids[] = {
 	{ .compatible = "fsl,vf610-dspi", .data = NULL, },
 	{ /* sentinel */ }
 };