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)