[POWERPC] scc_sio: Fix link failure

scc_sio.o should only be built if the txx9 serial driver is actually
built into the kernel.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

--
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/celleb/Makefile

@@ -4,5 +4,5 @@ obj-y				+= interrupt.o iommu.o setup.o \
 
 obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_PPC_UDBG_BEAT)	+= udbg_beat.o
-obj-$(CONFIG_HAS_TXX9_SERIAL)	+= scc_sio.o
+obj-$(CONFIG_SERIAL_TXX9)	+= scc_sio.o
 obj-$(CONFIG_SPU_BASE)		+= spu_priv1.o