ARM: dts: aspeed: add missing memory unit-address

The base aspeed-g5.dtsi already defines a '/memory@80000000' node, so
'/memory' in the board files create a duplicate node. We're probably
getting lucky that the bootloader fixes up the memory node that the
kernel ends up using. Add the unit-address so it's merged with the base
node.

Found with DT json-schema checks.

Cc: Joel Stanley <joel@jms.id.au>
Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: devicetree@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-aspeed@lists.ozlabs.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Olof Johansson <olof@lixom.net>