drm/i915: Remove the broken flush_ring from page-flip

This is already performed with the pipelined flush, so by the time we
schedule the flush in the page-flip, the ring is NULL and we OOPs
instead.

Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3fd69ad..174e38a 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1924,7 +1924,7 @@
 	return i915_do_wait_request(dev, seqno, 1, ring);
 }
 
-void
+static void
 i915_gem_flush_ring(struct drm_device *dev,
 		    struct drm_file *file_priv,
 		    struct intel_ring_buffer *ring,