media: s5p-mfc: Corrected NV12M/NV21M plane-sizes

There is a possibility of getting page fault if the overall
buffer size is not aligned to 256bytes. Since MFC does read
operation only and it won't corrupt the data values even if
it reads the extra bytes.
Corrected luma and chroma plane sizes for V4L2_PIX_FMT_NV12M
and V4L2_PIX_FMT_NV21M pixel format.

Suggested-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Aakarsh Jain <aakarsh.jain@samsung.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>