spi: fix use of set_cs in spi_s3c24xx driver

It turns out that the last patch to change set_cs to be kept in the
controller's structure instead of the platform data was an incomplete
change, and did not change the references to platfrom data in the setup
xfer code.  (This can prevent an oops.)

Reported-by:  <Ling.Alex@iac.com.tw>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>