ARM: dts: meson8m2: update the offset of the canvas module

With the Meson8m2 SoC the canvas module was moved from offset 0x20
(Meson8) to offset 0x48 (same as on Meson8b). The offsets inside the
canvas module are identical.

Correct the offset so the driver uses the correct registers.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>