dts: arm: st: f4: fix die_temp channel

The STM32F4 socs have different channels for the temperature sensor.
Some are at channel 16 and some at channel 18. Made changes wherever it
was relevant.
In short, the base configuration is to channel 16 and wherever it is
supposed to be 18 it is overridden.

Signed-off-by: Yishai Jaffe <yishai1999@gmail.com>