ARM: dts: exynos: Fix watchdog reset on Exynos4412

The Exynos4412 has the same watchdog as newer SoCs (e.g. Exynos5250).
Just like the others, for working it requires additional steps in Power
Management Unit: unmasking the reset request and enabling the system
reset.  Without these additional steps in PMU, the watchdog will not be
able to reset the system on expiration event.

Change the compatible of Exynos4412 watchdog device node to
samsung,exynos5250-wdt which includes the additional PMU steps.

This will also fix infinite watchdog interrupt in soft mode (lack of
interrupt clear) because it is also included in samsung,exynos5250-wdt.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>