watchdog: Fix omap watchdogs to enable the magic close bit

This allows testing the watchdog easily with distros just by
doing pkill -9 watchdog.

Reported-by: Thomas Dziedzic <gostrc@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>