thermal: da9062/61: Prevent hardware access during system suspend

The workqueue used for monitoring the hardware may run while the device
is already suspended.  Fix this by using the freezable system workqueue
instead, cfr. commit 51e20d0e ("thermal: Prevent polling from
happening during system suspend").

Fixes: 608567aa ("thermal: da9062/61: Thermal junction temperature monitoring driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Steve Twiss <stwiss.opensource@diasemi.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>