dri2: fix potential loop issue with triple buffer flip
dri2: fix potential loop issue with triple buffer flip

Signed-off-by: Rob Clark <915c10c999604870200b6defbe633d857c856ca0@gmail.com>

freedesktop-unofficial-mirror/xorg__driver__xf86-video-omap,robclark/xf86-video-omap,robclark/xf86-video-omap,rcn-ee/xf86-video-omap,RobertCNelson/xf86-video-omap,rcn-ee/xf86-video-omap,freedesktop-unofficial-mirror/xorg__driver__xf86-video-omap,RobertCNelson/xf86-video-omap