volume-tile: Set fixed size for the "mute" checkbox
volume-tile: Set fixed size for the "mute" checkbox

Fixes: BMC#13569 - The box of mute on device panel shows unfriendly

meego-netbook-ux/meego-panel-devices,meego-netbook-ux/meego-panel-devices,meego-netbook-ux/meego-panel-devices