drm/radeon: async event synchronization for drmWaitVblank

Bring radeon up to speed with the async event synchronization for
drmWaitVblank. See c9a9c5e02aedc1a2815877b0268f886d2640b771 for
more information. Without this patch event never get delivered
to userspace client.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_drv.c

@@ -216,6 +216,7 @@ static struct drm_driver driver_old = {
 		 .mmap = drm_mmap,
 		 .poll = drm_poll,
 		 .fasync = drm_fasync,
+		 .read = drm_read,
 #ifdef CONFIG_COMPAT
 		 .compat_ioctl = radeon_compat_ioctl,
 #endif
@@ -304,6 +305,7 @@ static struct drm_driver kms_driver = {
 		 .mmap = radeon_mmap,
 		 .poll = drm_poll,
 		 .fasync = drm_fasync,
+		 .read = drm_read,
 #ifdef CONFIG_COMPAT
 		 .compat_ioctl = radeon_kms_compat_ioctl,
 #endif