[WATCHDOG] hpwdt - fix lower timeout limit

[Novell Bug 581103] HP Watchdog driver has arbitrary (wrong) timeout limits.
Fix the lower timeout limit to a more appropriate value.

Signed-off-by: Thomas Mingarelli <Thomas.Mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Cc: stable <stable@kernel.org>