watchdog: omap: don't disable the timer when it should be enabled early

With the early_enable module parameter the watchdog can be started
during driver probe time. If this is requested the bets are good that
the timer is already running, so to narrow the gap where the timer is
disabled only call the disable function when the timer shouldn't be
started.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>