drm/i915: Complete pending resets before get-reset-stats ioctl

The get-reset-stats ioctls wasn't waiting for a pending reset before
reporting its statistics, and so was ignoring a hang generated by the
context that should have been reported against said context.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Tested-by: NMika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463137042-9669-2-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -1056,7 +1056,7 @@ int i915_gem_context_reset_stats_ioctl(struct drm_device *dev,
 	if (args->ctx_id == DEFAULT_CONTEXT_HANDLE && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	ret = i915_mutex_lock_interruptible(dev);
 	if (ret)
 		return ret;