spi: tegra20-slink: 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-slink.c

···
 	.cs_hold_time = false,
 };
 
-static struct of_device_id tegra_slink_of_match[] = {
+static const struct of_device_id tegra_slink_of_match[] = {
 	{ .compatible = "nvidia,tegra30-slink", .data = &tegra30_spi_cdata, },
 	{ .compatible = "nvidia,tegra20-slink", .data = &tegra20_spi_cdata, },
 	{}