[ARM] S3C24XX: Fix indentation in <plat/dma-regs.h>

The <plat/dma-regs.h> pre-date the invention of the TAB character,
so fix the indentation of the register defines.
Signed-off-by: NBen Dooks <ben@simtec.co.uk>
Signed-off-by: NBen Dooks <ben-linux@fluff.org>