imx: Fix critical thermal threshold

imx: Fix critical thermal threshold

Fix the critical thermal threshold for i.MX processors, this was changed
while moving the code from imx8m/imx9 directories into a shared place.

There is no need to keep the critical threshold 5 degrees less than the
SoC maximum temperature threshold, what is actually going to happen in
practice is that we are going to power-off the board when the SoC is
still within its working temperature range.

In addition to that this is a change in the actual behavior, that is
introducing a regression to users, and it was hidden within a software
refactoring.

Fixes: d0fe80890ab1 ("imx: Generalize fixup_thermal_trips")
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>