After r285994, sysctl(8) was fixed to use 273.15 instead of 273.20 as 0C
reference and as result, the temperature read in sysctl(8) now exibits a
+0.1C difference.
This commit fix the kernel references to match the reference value used in
sysctl(8) after r285994.
Sponsored by: Rubicon Communications (Netgate)
I2C real-time clock (RTC).
The DS3231 has an integrated temperature-compensated crystal oscillator
(TXCO) and crystal.
DS3231 has a temperature sensor, an independent 32kHz output (which can be
turned on and off by the driver) and another output that can be used as
interrupt for alarms or as a second square-wave output, which frequency and
operation mode can be set by driver sysctl(8) knobs.
Differential Revision: https://reviews.freebsd.org/D1016
Reviewed by: ian, rpaulo
Tested on: Raspberry pi model B
