handle polling when cold in tipmic_thermal_opreg_handler().

handle polling when cold in tipmic_thermal_opreg_handler().

this allows me to boot if acpitz is using tipmic instead of getting
stuck. tipmic would spin on tsleep, which returns immediately with
0 when cold, waiting for a value to be set by the tipmic interrupt
handler. cos the box is cold the interrupt is masked, so the tsleep
loop never ended.

patrick@ helped me find this
ok kettenis@