rtc: ds3232: fix call trace when rtc->ops_lock is used as NULL

The rtc->ops_lock would be accessed in ds3232_irq() without being
initialized as rtc_device_register() is called too late.

So move devm_rtc_device_register() just before registering irq handler
to initialize rtc->ops_lock earlier.

Signed-off-by: Gong Qianyu <Qianyu.Gong@nxp.com>
Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>