[media] s5p-jpeg: Adjust buffer size for Exynos 4412

Eliminate iommu fault during encoding by adjusting image size
used for buffer size computation and ensuring that the buffer
is not overrun.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>