fs: dlm: cleanup STOP_IO bitflag set when stop io

There should no difference between setting the CF_IO_STOP flag
before restore_callbacks() to do it before or afterwards. The
restore_callbacks() will be sure that no callback is executed anymore
when the bit wasn't set.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>