ui/cocoa.m: addRemovableDevicesMenuItems() warning fix

Eliminate this warning associated with the addRemovableDevicesMenuItems()
function:

ui/cocoa.m:1344:13: warning: function declaration isn't a prototype
[-Wstrict-prototypes]
 static void addRemovableDevicesMenuItems()
             ^
ui/cocoa.m: In function 'addRemovableDevicesMenuItems':
ui/cocoa.m:1344:13: warning: old-style function definition [-Wold-style-definition]
Signed-off-by: NJohn Arbuckle <programmingkidx@gmail.com>
Message-id: 7B365FC2-072B-4E8D-A1D9-922C2D691A83@gmail.com
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

ui/cocoa.m

@@ -1353,7 +1353,7 @@ static void add_console_menu_entries(void)
 /* Make menu items for all removable devices.
  * Each device is given an 'Eject' and 'Change' menu item.
  */
-static void addRemovableDevicesMenuItems()
+static void addRemovableDevicesMenuItems(void)
 {
     NSMenu *menu;
     NSMenuItem *menuItem;