Cocoa: Silence warning for cocoa_keycode_to_qemu

Make cocoa_keycode_to_qemu static, to avoid:

warning: no previous prototype for ‘cocoa_keycode_to_qemu’
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Cc: John Arbuckle <programmingkidx@gmail.com>
Signed-off-by: Nmalc <av1474@comtv.ru>

cocoa.m

@@ -233,7 +233,7 @@ int keymap[] =
 */
 };
 
-int cocoa_keycode_to_qemu(int keycode)
+static int cocoa_keycode_to_qemu(int keycode)
 {
     if((sizeof(keymap)/sizeof(int)) <= keycode)
     {