mfd: ab8500-sysctrl: Set sysctrl_dev during probe

The driver requires sysctrl_dev to be set at probe, as it's used by
other driver functions.  This was dropped by mistake in:

2377e52f mfd: ab8500-sysctrl: Error check clean up

making all driver functions fail.
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/ab8500-sysctrl.c

@@ -191,6 +191,8 @@ static int ab8500_sysctrl_probe(struct platform_device *pdev)
 	if (!(plat && plat->sysctrl))
 		return -EINVAL;
 
+	sysctrl_dev = &pdev->dev;
+
 	if (plat->pm_power_off)
 		pm_power_off = ab8500_power_off;