hwmon: (coretemp) Allow format checking

By extracting the only part that differs we can allow static checking
of the format string, and possibly save a little .rodata.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
[Guenter Roeck: continuation line alignment]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>