drm/i915: Fix context locking in debugfs

This goes all the way back to the introduction of this debugfs file,
even though back then no locking really was required. None of the
intermediate patches fixed this.
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1721,7 +1721,7 @@ static int i915_context_status(struct seq_file *m, void *unused)
 	struct intel_context *ctx;
 	int ret, i;
 
-	ret = mutex_lock_interruptible(&dev->mode_config.mutex);
+	ret = mutex_lock_interruptible(&dev->struct_mutex);
 	if (ret)
 		return ret;
 
@@ -1751,7 +1751,7 @@ static int i915_context_status(struct seq_file *m, void *unused)
 		seq_putc(m, '\n');
 	}
 
-	mutex_unlock(&dev->mode_config.mutex);
+	mutex_unlock(&dev->struct_mutex);
 
 	return 0;
 }