drm/vblank: Use u32 consistently for vblank counters

In

commit 99264a61df
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Apr 15 19:34:43 2015 +0200

    drm/vblank: Fixup and document timestamp update/read barriers

I've switched vblank->count from atomic_t to unsigned long and
accidentally created an integer comparison bug in
drm_vblank_count_and_time since vblanke->count might overflow the u32
local copy and hence the retry loop never succeed.

Fix this by consistently using u32.

Cc: Michel Dänzer <michel@daenzer.net>
Reported-by: Michel Dänzer <michel@daenzer.net>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/drm_irq.c

@@ -75,7 +75,7 @@ module_param_named(timestamp_precision_usec, drm_timestamp_precision, int, 0600)
 module_param_named(timestamp_monotonic, drm_timestamp_monotonic, int, 0600);
 
 static void store_vblank(struct drm_device *dev, int crtc,
-			 unsigned vblank_count_inc,
+			 u32 vblank_count_inc,
 			 struct timeval *t_vblank)
 {
 	struct drm_vblank_crtc *vblank = &dev->vblank[crtc];

include/drm/drmP.h

@@ -691,7 +691,7 @@ struct drm_vblank_crtc {
 	struct timer_list disable_timer;		/* delayed disable timer */
 
 	/* vblank counter, protected by dev->vblank_time_lock for writes */
-	unsigned long count;
+	u32 count;
 	/* vblank timestamps, protected by dev->vblank_time_lock for writes */
 	struct timeval time[DRM_VBLANKTIME_RBSIZE];