spi_s3c24xx: fix header includes

The driver includes <asm/io.h> where it should be including <linux/io.h>
and also includes <mach/hardware.h> and <asm/dma.h> without using anything
from these.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>