Fix this set but not used warning:

drivers/s390/cio/vfio_ccw_drv.c: In function 'vfio_ccw_sch_io_todo':
drivers/s390/cio/vfio_ccw_drv.c:72:21: warning: variable 'sch' set but not used [-Wunused-but-set-variable]
  struct subchannel *sch;
                     ^
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>