ARM: S3C64XX: DMA: Make src and dst transfer size same

Some devices don't seem to work if the source and desitnation transfer
widths are not same. For example, SPI dma xfers, with 8bits/word,
don't work without this patch.

Signed-off-by: Jassi Brar <jassi.brar@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>