drm/msm: Disallow submit with fence id 0

A fence id of zero is expected to be invalid, and is not removed from
the fence_idr table.  If userspace is requesting to specify the fence
id with the FENCE_SN_IN flag, we need to reject a zero fence id value.

Fixes: 17154add ("drm/msm: Add MSM_SUBMIT_FENCE_SN_IN")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/549180/

drivers/gpu/drm/msm/msm_gem_submit.c

@@ -901,7 +901,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 	 * after the job is armed
 	 */
 	if ((args->flags & MSM_SUBMIT_FENCE_SN_IN) &&
-			idr_find(&queue->fence_idr, args->fence)) {
+			(!args->fence || idr_find(&queue->fence_idr, args->fence))) {
 		spin_unlock(&queue->idr_lock);
 		idr_preload_end();
 		ret = -EINVAL;