ARM: dts: Specify MAX77686 pmic interrupt for exynos5250-smdk5250

The IRQB interrupt pin of MAX77686 PMIC is connected to GPX3[2] pin of
Exynos5250 on the Exynos5250 SMDK board. Specify this connection using
interrupts property for the max77686 pmic node.

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>