drm/vc4: Fix leak of the file_priv that stored the perfmon.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: 65101d8c9108 ("drm/vc4: Expose performance counters to userspace")
Link: https://patchwork.freedesktop.org/patch/msgid/20180409205813.7077-1-eric@anholt.net
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>

drivers/gpu/drm/vc4/vc4_drv.c

@@ -130,6 +130,7 @@ static void vc4_close(struct drm_device *dev, struct drm_file *file)
 	struct vc4_file *vc4file = file->driver_priv;
 
 	vc4_perfmon_close_file(vc4file);
+	kfree(vc4file);
 }
 
 static const struct vm_operations_struct vc4_vm_ops = {