thermal: rcar_gen3_thermal: update max temperature clamp

Change the upper limit to clamp the high temperature value to 120C when
setting trip points.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>