arm64: dts: amlogic: meson-g12: Fix thermal-zones indent

This node is currently at /soc/thermal-zones, but the later introduced
bindings in commit 1202a442 ("dt-bindings: thermal: Add yaml bindings
for thermal zones") put this at /thermal-zones.
Fix dtb_check warning by moving the thermal-zones node to /

Signed-off-by: Alexander Stein <alexander.stein@mailbox.org>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20211026182813.900775-1-alexander.stein@mailbox.org