spi: fix spi_s3c24xx_gpio num_chipselect

The spi master driver must have num_chipselect set to allow the bus to
initialise.  Pass this through the platform data.

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>