arm64: dts: renesas: r8a77961: salvator-xs: Fix memory unit-address

Correct the unit-address of the second memory node, to match the
corresponding reg property.

Fixes: 92980759

 ("arm64: dts: renesas: Add support for Salvator-XS with R-Car M3-W+")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200309170825.20882-1-geert+renesas@glider.be