qxl_close_screen: disable fb access, prevent segfaults in uxa later on
qxl_close_screen: disable fb access, prevent segfaults in uxa later on

I don't have a stacktrace to show any segfault unfortunately.

dezelin/xf86-video-qxl,fgouget/xf86-video-qxl,dezelin/xf86-video-qxl,facboy/xserver-xorg-video-qxl,facboy/xserver-xorg-video-qxl,fgouget/xf86-video-qxl,facboy/xserver-xorg-video-qxl,fgouget/xf86-video-qxl,facboy/xserver-xorg-video-qxl,fgouget/xf86-video-qxl,dezelin/xf86-video-qxl