drivers/ata/Kconfig: PATA_SCC depends on wrong platform

PATA_SCC depends on PPC_CELLEB. (not PPC_IBM_CELL_BLADE)

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Signed-off-by: Akira Iguchi <akira2.iguchi@toshiba.co.jp>
Signed-off-by: Jeff Garzik <jeff@garzik.org>