exynos4: gralloc: update constant to match mali r4p0

As defined here https://github.com/NamelessRom/android_kernel_samsung_smdk4412/blob/android-4.4/drivers/gpu/mali400/r4p0/ump/include/ump_uk_types.h#L57

Change-Id: Ia4ccf15143a6575def528acef9a20e86710b18f4