thermal: rcar_gen3_thermal: Fix to show correct trip points number

Currently after store trip points number in 'ret', it is overwritten
afterwards, this cause incorrect trip point number always be shown in
the debug information after register of each thermal zone.

This patch fix this issue by moving get of trip number to
end of thermal zone registration.

Fixes: 6269e9f7 ("thermal: rcar_gen3_thermal: Register hwmon sysfs interface")
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>