dix: free the sprite when disabling the device

Disabled devices don't need sprites (they can't send events anyway) and the
device init process is currently geared to check for whether sprite is
present to check if the device should be paired/attached.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>

dix/devices.c

@@ -465,6 +465,8 @@ DisableDevice(DeviceIntPtr dev, BOOL sendevent)
     (void) (*dev->deviceProc) (dev, DEVICE_OFF);
     dev->enabled = FALSE;
 
+    FreeSprite(dev);
+
     /* now that the device is disabled, we can reset the signal handler's
      * last.slave */
     OsBlockSignals();