thermal: imx_tmu: Fix for temperature out of range

When the temperature is out of sensor's range, the Valid bit won't be
set in TRITSR register. So the polling loop won't go out.

Change the codes to retry 10 times with 100ms interval for the Valid bit.
If the timeout, we give a warning for the invalid data.

Modifed from Ye's NXP patch

Signed-off-by: Peng Fan <peng.fan@nxp.com>