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 <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-tegra20-sflash.c

···
 	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", },
 	{}
 };