viocd: needs to depend on BLOCK

Fix this build error when CONFIG_BLOCK is not set:
drivers/cdrom/viocd.c: In function 'viocd_blk_open':
drivers/cdrom/viocd.c:156: error: dereferencing pointer to incomplete type
drivers/cdrom/viocd.c: In function 'viocd_blk_release':
drivers/cdrom/viocd.c:162: error: dereferencing pointer to incomplete type
drivers/cdrom/viocd.c: In function 'viocd_blk_ioctl':
drivers/cdrom/viocd.c:170: error: dereferencing pointer to incomplete type
drivers/cdrom/viocd.c: In function 'viocd_blk_media_changed':
drivers/cdrom/viocd.c:176: error: dereferencing pointer to incomplete type
...

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

arch/powerpc/platforms/iseries/Kconfig

@@ -17,6 +17,7 @@ config VIODASD
 
 config VIOCD
 	tristate "iSeries Virtual I/O CD support"
+	depends on BLOCK
 	select VIOPATH
 	help
 	  If you are running Linux on an IBM iSeries system and you want to