rk_tsadc: use tsadc_temp_to_raw for shutdown_temp
Use tsadc_temp_to_raw instead of tsadc_raw_to_temp, otherwise rk3566/68
get stuck in a kernel reboot cycle.
https://forums.freebsd.org/threads/running-freebsd-on-radxa-rock-3c-rk3566-board.89389/post-624890
Submitted by: covacat
Reviewed by: mmel
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D52309
(cherry picked from commit 2b0f8c6907b96a8e150a1250e56d25a7a5d202d8)