drm/tilcdc: mark symbols static where possible

We get 3 warnings when building kernel with W=1:
drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c:142:29: warning: no previous prototype for 'tilcdc_get_overlay' [-Wmissing-prototypes]
drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c:198:13: warning: no previous prototype for 'tilcdc_convert_slave_node' [-Wmissing-prototypes]
drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c:264:12: warning: no previous prototype for 'tilcdc_slave_compat_init' [-Wmissing-prototypes]

In fact, these functions are only used in the file in which they are
declared and don't need a declaration, but can be made static.
So this patch marks these functions with 'static'.
Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Jyri Sarha <jsarha@ti.com>

drivers/gpu/drm/tilcdc/tilcdc_slave_compat.c

@@ -139,7 +139,7 @@ static void __init tilcdc_node_disable(struct device_node *node)
 	of_update_property(node, prop);
 }
 
-struct device_node * __init tilcdc_get_overlay(struct kfree_table *kft)
+static struct device_node * __init tilcdc_get_overlay(struct kfree_table *kft)
 {
 	const int size = __dtb_tilcdc_slave_compat_end -
 		__dtb_tilcdc_slave_compat_begin;
@@ -195,7 +195,7 @@ static const char * const tilcdc_slave_props[] __initconst = {
 	NULL
 };
 
-void __init tilcdc_convert_slave_node(void)
+static void __init tilcdc_convert_slave_node(void)
 {
 	struct device_node *slave = NULL, *lcdc = NULL;
 	struct device_node *i2c = NULL, *fragment = NULL;
@@ -261,7 +261,7 @@ void __init tilcdc_convert_slave_node(void)
 	of_node_put(fragment);
 }
 
-int __init tilcdc_slave_compat_init(void)
+static int __init tilcdc_slave_compat_init(void)
 {
 	tilcdc_convert_slave_node();
 	return 0;