ui/cocoa: Send warning message to stderr, not stdout

Bring a warning message into line with the others in this file by
sending it to stderr, not stdout.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1386543546-31919-4-git-send-email-peter.maydell@linaro.org

ui/cocoa.m

@@ -239,7 +239,7 @@ int keymap[] =
 static int cocoa_keycode_to_qemu(int keycode)
 {
     if (ARRAY_SIZE(keymap) <= keycode) {
-        printf("(cocoa) warning unknown keycode 0x%x\n", keycode);
+        fprintf(stderr, "(cocoa) warning unknown keycode 0x%x\n", keycode);
         return 0;
     }
     return keymap[keycode];