hwmon: (coretemp) Do not return -EAGAIN for low temperatures

Some Intel CPUs do not set the 'valid' bit in IA32_THERM_STATUS if the
temperature is too low to be measured. This condition will not change until
the CPU is hot enough for its temperature to be measured. Returning an error
in such conditions is not very useful. Drop checking the valid bit and just
return the reported temperature instead.

Reviewed-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>