Change internal temperature base from -267.7C to -243.7C. The AXP223
datasheet says that the value is between -267.7C and 165.8C in steps of 0.1C,
but this doesn't make sense for a 12-bit field. If we take the maximum value
and subtract 4095 we get -243.7C, effectively adding +24C to the reported
temp. On my A31 board, this changes a chilly 15.3C to a more reasonable 39.3C.
Explicitly compare to NULL to show clang that the bool conversion is
intentional, even if it is always true in case of the arrays.
Preserve const.
No reason not to make the string const.