dts: arm: stih418: Fix complain about IRQ_TYPE_NONE usage

Since commit 83a86fbb ("irqchip/gic: Loudly complain about the use of IRQ_TYPE_NONE")
kernel is complaining about the IRQ_TYPE_NONE usage which shouldn't
be used.

Use IRQ_TYPE_LEVEL_HIGH instead.

Signed-off-by: Alain Volmat <avolmat@me.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>