mkimage: added 'static' specifier to match function's prototype.

This function should be declared static.

Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>
Signed-off-by: Simon Glass <sjg@chromium.org>

tools/mkimage.c

@@ -632,8 +632,7 @@ copy_file (int ifd, const char *datafile, int pad)
 	(void) close (dfd);
 }
 
-void
-usage ()
+static void usage(void)
 {
 	fprintf (stderr, "Usage: %s -l image\n"
 			 "          -l ==> list image header information\n",