ARM: dts: aspeed: Fix hwrng register address

The register address should be the full address of the rng, not the
offset from the start of the SCU.

Fixes: 5daa8212 ("ARM: dts: aspeed: Describe random number device")
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Olof Johansson <olof@lixom.net>