fbdev: prevent assertion in debug mode
fbdev: prevent assertion in debug mode

There are places in DirectFB which D_ASSUME() the lock's offset and the
allocation's offset to be identical, being verbose if that's not the
case.

dfbdok/DirectFB1,DirectFB/directfb,sklnet/DirectFB,DirectFB/directfb,deniskropp/DirectFB,deniskropp/DirectFB,kaostao/directfb,dfbdok/DirectFB1,DirectFB/directfb,lancebaiyouview/DirectFB,djbclark/directfb-core-DirectFB,kevleyski/directfb,sklnet/DirectFB,Distrotech/DirectFB,jcdubois/DirectFB,dfbdok/DirectFB1,kevleyski/DirectFB-1,kevleyski/DirectFB-1,kevleyski/directfb,djbclark/directfb-core-DirectFB,deniskropp/DirectFB,djbclark/directfb-core-DirectFB,lancebaiyouview/DirectFB,lancebaiyouview/DirectFB,Distrotech/DirectFB,Distrotech/DirectFB,kaostao/directfb,jcdubois/DirectFB,sklnet/DirectFB,kaostao/directfb,djbclark/directfb-core-DirectFB,kevleyski/directfb,mtsekm/test,kevleyski/DirectFB-1,mtsekm/test,sklnet/DirectFB,jcdubois/DirectFB,lancebaiyouview/DirectFB,kevleyski/directfb,kevleyski/DirectFB-1,deniskropp/DirectFB,mtsekm/test