iTCO_wdt: fix TCO V1 timeout values and limits

For TCO V1 devices the programmed timeout was twice too long
because the fact that the TCO V1 timer needs to count down
twice before triggering the watchdog, wasn't accounted for.
Also the timeout values in the module description and error
message were clarified. And the _STS registers are 16 bit
instead of 8 bit.

Signed-off-by: Pádraig Brady <P@draigBrady.com>
Tested-by: Simon Kagstrom <simon.kagstrom@netinsight.se>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>