spi: tegra20-sflash: 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-tegra20-sflash.c

@@ -419,7 +419,7 @@ static irqreturn_t tegra_sflash_isr(int irq, void *context_data)
 	return handle_cpu_based_xfer(tsd);
 }
 
-static struct of_device_id tegra_sflash_of_match[] = {
+static const struct of_device_id tegra_sflash_of_match[] = {
 	{ .compatible = "nvidia,tegra20-sflash", },
 	{}
 };