ipmi:watchdog: Set panic count to proper value on a panic

You will get two decrements when the messages on a panic are sent, not
one, since commit 2033f685 ("ipmi: Free receive messages when in an
oops") was added, but the watchdog code had a bug where it didn't set
the value properly.

Reported-by: Anton Lundin <glance@acc.umu.se>
Cc: <Stable@vger.kernel.org> # v5.4+
Fixes: 2033f685 ("ipmi: Free receive messages when in an oops")
Signed-off-by: Corey Minyard <cminyard@mvista.com>