arm64: dts: mediatek: mt8516-pumpkin: Fix machine compatible

arm64: dts: mediatek: mt8516-pumpkin: Fix machine compatible

This devicetree contained only the SoC compatible but lacked the
machine specific one: add a "mediatek,mt8516-pumpkin" compatible
to the list to fix dtbs_check warnings.

Fixes: 9983822c8cf9 ("arm64: dts: mediatek: add pumpkin board dts")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Fei Shao <fshao@chromium.org>
Link: https://lore.kernel.org/r/20250724083914.61351-39-angelogioacchino.delregno@collabora.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>