ARM: S3C: Fix NAND device registration by s3c_nand_set_platdata().

Fix two bugs in s3c_nand_set_platdata() where thet device's platform
data was not set, and the wrong error check was being performed on
the return of s3c_nand_copy_set().

Fixes the following OOPS:

Unable to handle kernel NULL pointer dereference at virtual address 00000004
PC is at s3c24xx_nand_probe+0x234/0x594

Signed-off-by: Ben Dooks <ben-linux@fluff.org>