drm/i915: Don't double-unpin buffers if we take a signal in evict_everything().

We haven't seen this in practice, but it was visible when looking at a bug
report from when i915_gem_evict_everything() was broken and would always
return error.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/gpu/drm/i915/i915_gem.c

@@ -2498,6 +2498,7 @@ i915_gem_execbuffer(struct drm_device *dev, void *data,
 		/* unpin all of our buffers */
 		for (i = 0; i < pinned; i++)
 			i915_gem_object_unpin(object_list[i]);
+		pinned = 0;
 
 		/* evict everyone we can from the aperture */
 		ret = i915_gem_evict_everything(dev);