minios: fix free_fbfront
minios: fix free_fbfront

When a stubdom is destroyed, fbfront tries to unbind the evtchn
twice.

Signed-off-by: Stefano Stabellini <22a0c6385d750d07aa383c9f813cf6f0228657d8@eu.citrix.com>

rowhit/xen-minios,rowhit/xen-minios,rowhit/xen-minios