'memory-region' is a common property, so it doesn't need a type ref here.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Alex Elder <elder@kernel.org>
Cc: netdev@vger.kernel.org
Acked-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20201222040121.1314370-1-robh@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>