bugfix: dlsim was not working anymore

When you ran it with the scope as:

    ./dlsim -X

you saw no activity in the "PDSCH I/Q of MF Output" window,
so matter what SNR you put (even for very high SNR, say: ./dlsim -X -s40)

this commit seems to fix it.

I am not sure it is the end of story. The 2 threads PDCCH/PDSCH structures
may still not be used correctly everywhere.

openair1/SIMULATION/LTE_PHY/dlsim.c

@@ -1998,7 +1998,7 @@ int main(int argc, char **argv)
     }
   */
 
-  UE->pdcch_vars[0][0]->crnti = n_rnti;
+  UE->pdcch_vars[subframe & 0x1][0]->crnti = n_rnti;
 
   // Fill in UL_alloc
   UL_alloc_pdu.type    = 0;