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

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