rtc: omap: Cut down the shutdown time from 2 seconds to 1 sec

Cut down the shutdown time from 2 seconds to 1 sec. In case of roll
over try again.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>