devmapper: Call UdevWait() even in failure path

Currently we set up a cookie and upon failure not call UdevWait(). This
does not cleanup the cookie and associated semaphore and system will
soon max out on total number of semaphores.

To avoid this, call UdevWait() even in failure path which in turn will
cleanup associated semaphore.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Vincent Batts <vbatts@redhat.com>