ARM: dts: Fixed typo interrupt-cells for exynos5420 and exynos5250

Changes fixes the misspelled of #interrups-cell.

arch/arm/boot/dts/exynos5420.dtsi:224: WARNING: 'interrups'
	 may be misspelled - perhaps 'interrupts'?

Tested on OdroidXU3 board.

Signed-off-by: Anand Moon <linux.amoon@gmail.com>
[kgene@kernel.org: added fixing same typo in exynos5250]
Signed-off-by: Kukjin Kim <kgene@kernel.org>