Fix dynamic decision for Scan and bug in Allreduce

Signed-off-by: Mikhail Kurnosov <mkurnosov@gmail.com>

ompi/mca/coll/base/coll_base_allreduce.c

@@ -1183,7 +1183,7 @@ int ompi_coll_base_allreduce_intra_redscat_allgather(
          * to recursive doubling (previous step).
          */
 
-        step--;
+        step = nsteps - 1;
 
         for (int mask = nprocs_pof2 >> 1; mask > 0; mask >>= 1) {
             int vdest = vrank ^ mask;

ompi/mca/coll/tuned/coll_tuned_decision_dynamic.c

@@ -690,7 +690,7 @@ int ompi_coll_tuned_scan_intra_dec_dynamic(const void *sbuf, void* rbuf, int cou
     if (tuned_module->user_forced[SCAN].algorithm) {
         return ompi_coll_tuned_scan_intra_do_this(sbuf, rbuf, count, dtype,
                                                   op, comm, module,
-                                                  tuned_module->user_forced[EXSCAN].algorithm);
+                                                  tuned_module->user_forced[SCAN].algorithm);
     }
 
     return ompi_coll_base_scan_intra_linear(sbuf, rbuf, count, dtype,