ARM: dts: sun4i: Rename thermal nodes to avoid warnings

The thermal-zone subnodes we defined for the A10 have underscores in them
that will generate DTC warnings. Change those underscores for hyphens.

Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>