drm/exynos: gsc: Increase Exynos5433 buffer width alignment to 16 pixels

Investigation revealed that GScaler hardware requires the real buffer width
(pitch) to be aligned to 16 pixels.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>