rtc: omap: fix potential crash on power off

Do not set the system power-off callback and omap power-off rtc pointer
until we're done setting up our device to avoid leaving stale pointers
around after a late probe error.

Fixes: 97ea1906 ("rtc: omap: Support ext_wakeup configuration")
Cc: stable <stable@vger.kernel.org>     # 4.9
Cc: Marcin Niestroj <m.niestroj@grinn-global.com>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-omap.c

@@ -861,13 +861,6 @@ static int omap_rtc_probe(struct platform_device *pdev)
 			goto err;
 	}
 
-	if (rtc->is_pmic_controller) {
-		if (!pm_power_off) {
-			omap_rtc_power_off_rtc = rtc;
-			pm_power_off = omap_rtc_power_off;
-		}
-	}
-
 	/* Support ext_wakeup pinconf */
 	rtc_pinctrl_desc.name = dev_name(&pdev->dev);
 
@@ -884,6 +877,13 @@ static int omap_rtc_probe(struct platform_device *pdev)
 
 	rtc_nvmem_register(rtc->rtc, &omap_rtc_nvmem_config);
 
+	if (rtc->is_pmic_controller) {
+		if (!pm_power_off) {
+			omap_rtc_power_off_rtc = rtc;
+			pm_power_off = omap_rtc_power_off;
+		}
+	}
+
 	return 0;
 
 err: