ARM: dts: update bootargs to boot from sda2 for exynos5440-ssdk5440

Updated the bootargs to boot the system with rootfs in /dev/sda2
instead of ramdisk.

Signed-off-by: Subash Patel <subash.rp@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>