[WATCHDOG] pcwd_usb.c - get heartbeat from dip switches

The PCWD cards normally use the heartbeat that is set via
the dip-switches of the card. There are only 3 switches,
thus 8 combinations that each have a certain heartbeat.
The card can however be programmed with a heartbeat from
1 till 65535 seconds. This is what our driver does: it
programs the heartbeat on the card.

There are however a lot of people that don't know that
we set the heartbeat of the watchdog card to the value
provided by the heartbeat module parameter. Instead they
think that the heartbeat value is the same as set by the
dip-switches.

This patch changes the driver so that at startup you can
take the heartbeat from the dip-switches. You do this
by setting the heartbeat module parameter to 0. This
patch also makes this the default behaviour.

Signed-off-by: Wim Van Sebroeck <wim@iguana.be>