zephyr: test: thermistor: Add cleanup function
zephyr: test: thermistor: Add cleanup function

Add cleanup function to the thermistor testsuite. During it, temperature
sensors are set to 27*C to not trigger any warnings about overheating.

BUG=None
TEST=zmake -D test test-drivers
BRANCH=None

Signed-off-by: Tomasz Michalec <a547db31280d14f095c760a23a7523d0b1e55fe6@semihalf.com>
Change-Id: I49f0773cf25fb245327b3a8b0ec8619d480ff746
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3805203
Tested-by: Tomasz Michalec <c064a6042954d4ba0805003dc021b76413ff1548@google.com>
Commit-Queue: Tomasz Michalec <c064a6042954d4ba0805003dc021b76413ff1548@google.com>
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec