dtc: Mark various internal functions static

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
diff --git a/scripts/dtc/libfdt/fdt_ro.c b/scripts/dtc/libfdt/fdt_ro.c
index fbbba44..22e6929 100644
--- a/scripts/dtc/libfdt/fdt_ro.c
+++ b/scripts/dtc/libfdt/fdt_ro.c
@@ -411,7 +411,7 @@
 					     &phandle, sizeof(phandle));
 }
 
-int _stringlist_contains(const char *strlist, int listlen, const char *str)
+static int _stringlist_contains(const char *strlist, int listlen, const char *str)
 {
 	int len = strlen(str);
 	const char *p;