drm: Remove drm_pending_event->pid

We might as well dump the drm_file pointer, that's about as useful
a cookie as the pid. Noticed while typing docs for drm_file and friends.

Since the only consumer of this is the tracepoints I think we can safely
change this - those tracepoints should not be uapi relevant at all. It
all goes back to

commit b9c2c9ae882f058084e13e339925dbf8d2d20271
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Thu Jul 1 16:48:09 2010 -0700

    drm: add per-event vblank event trace points

which doesn't give a special justification for using pid over a pointer.

Also note that the nouveau code setting it is entirely pointless:
Since this isn't a vblank event, it will never hit the vblank
tracepoints.

Cc: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170308141257.12119-11-daniel.vetter@ffwll.ch
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 1906723..9bdca69 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -978,7 +978,7 @@ static void send_vblank_event(struct drm_device *dev,
 	e->event.tv_sec = now->tv_sec;
 	e->event.tv_usec = now->tv_usec;
 
-	trace_drm_vblank_event_delivered(e->base.pid, e->pipe,
+	trace_drm_vblank_event_delivered(e->base.file_priv, e->pipe,
 					 e->event.sequence);
 
 	drm_send_event_locked(dev, &e->base);
@@ -1505,7 +1505,6 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
 	}
 
 	e->pipe = pipe;
-	e->base.pid = current->pid;
 	e->event.base.type = DRM_EVENT_VBLANK;
 	e->event.base.length = sizeof(e->event);
 	e->event.user_data = vblwait->request.signal;
@@ -1534,7 +1533,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
 	DRM_DEBUG("event on vblank count %u, current %u, crtc %u\n",
 		  vblwait->request.sequence, seq, pipe);
 
-	trace_drm_vblank_event_queued(current->pid, pipe,
+	trace_drm_vblank_event_queued(file_priv, pipe,
 				      vblwait->request.sequence);
 
 	e->event.sequence = vblwait->request.sequence;