drm/i915: Ringbuffer signal func for the second BSD ring

This is missing in:

commit 78325f2d270897c9ee0887125b7abb963eb8efea
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Tue Apr 29 14:52:29 2014 -0700

    drm/i915: Virtualize the ringbuffer signal func

Looks to me like a rebase side-effect...

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -2186,6 +2186,7 @@ int intel_init_bsd2_ring_buffer(struct drm_device *dev)
 	ring->dispatch_execbuffer =
 			gen8_ring_dispatch_execbuffer;
 	ring->semaphore.sync_to = gen6_ring_sync;
+	ring->semaphore.signal = gen6_signal;
 	/*
 	 * The current semaphore is only applied on the pre-gen8. And there
 	 * is no bsd2 ring on the pre-gen8. So now the semaphore_register