drm/radeon: return an error if there is nothing to wait for

Otherwise the sa managers out of memory
handling doesn't work.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_fence.c

@@ -331,7 +331,7 @@ static int radeon_fence_wait_any_seq(struct radeon_device *rdev,
 
 	/* nothing to wait for ? */
 	if (ring == RADEON_NUM_RINGS) {
-		return 0;
+		return -ENOENT;
 	}
 
 	while (!radeon_fence_any_seq_signaled(rdev, target_seq)) {