drm/i915: Fix use of invalid array size for ring->sync_seqno

There are I915_NUM_RINGS-1 inter-ring synchronisation counters, but we
were clearing I915_NUM_RINGS of them. Oops.
Reported-by: NJiri Slaby <jirislaby@gmail.com>
Tested-by: NJiri Slaby <jirislaby@gmail.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem.c

@@ -1857,7 +1857,7 @@ i915_gem_retire_requests_ring(struct drm_device *dev,
 
 	seqno = ring->get_seqno(ring);
 
-	for (i = 0; i < I915_NUM_RINGS; i++)
+	for (i = 0; i < ARRAY_SIZE(ring->sync_seqno); i++)
 		if (seqno >= ring->sync_seqno[i])
 			ring->sync_seqno[i] = 0;
 

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -1175,7 +1175,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 		goto err;
 
 	seqno = i915_gem_next_request_seqno(dev, ring);
-	for (i = 0; i < I915_NUM_RINGS-1; i++) {
+	for (i = 0; i < ARRAY_SIZE(ring->sync_seqno); i++) {
 		if (seqno < ring->sync_seqno[i]) {
 			/* The GPU can not handle its semaphore value wrapping,
 			 * so every billion or so execbuffers, we need to stall