dlm: increment ls_count for dlm_scand

Increment the ls_count value while dlm_scand is processing a
lockspace so that release_lockspace()/remove_lockspace() will
wait for dlm_scand to finish.

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