[erts] Fix cpool_delete()

When setting modification marker on the 'prev' field of a carrier to
delete from a pool, we back off and wait for the content of the
field to receive expected value if it did not have that from the
beginning. Due to a copy-paste bug; when this happened, we waited on
a completely different memory location which caused the scheduler
thread doing this to get stuck forever. This is obviously a very
rare scenario, since this bug has been present for 11 years without
being reported.

erts/emulator/beam/erl_alloc_util.c

@@ -3479,7 +3479,7 @@ cpool_delete(Allctr_t *allctr, Allctr_t *prev_allctr, Carrier_t *crr)
 	b = 1;
 	do {
 	    b = backoff(b);
-	    tmp = cpool_read(&cpd2p->prev);
+	    tmp = cpool_read(&crr->cpool.prev);
 	} while (tmp != val);
     }