ARM64: dts: meson: uart: fix address space range

The address space range is actually 0x18, fixed here.

Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>