thermal/of: Remove of_thermal_get_ntrips()

The thermal OF code uses the generic trip points to initialize the
thermal zone. Consequently thermal_zone_get_num_trips() can be used
and the of_thermal_get_ntrips() is no longer needed. Remove it.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20221003092602.1323944-17-daniel.lezcano@linaro.org