Documentation/vm/page-types.c: Declare checked_open static

Nothing outside of Documentation/vm/page-types.c references
checked_open.
Signed-off-by: Josh Triplett <josh@joshtriplett.org>

Documentation/vm/page-types.c

@@ -218,7 +218,7 @@ static void fatal(const char *x, ...)
 	exit(EXIT_FAILURE);
 }
 
-int checked_open(const char *pathname, int flags)
+static int checked_open(const char *pathname, int flags)
 {
 	int fd = open(pathname, flags);