qxl: fix access to qxl ring
qxl: fix access to qxl ring

This really needs to be volatile as the hw will change it underneath
us. Really we should be using proper MMIO accessors for this stuff
not casting structs to mmio memory.

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