fix parallel sort key size

Author: Ehsan Totoni

hpat/hiframes/sort.py

@@ -421,7 +421,7 @@ def local_sort(key_arrs, data, ascending=True):
 
 @numba.njit(no_cpython_wrapper=True, cache=True)
 def parallel_sort(key_arrs, data, ascending=True):
-    n_local = len(key_arrs)
+    n_local = len(key_arrs[0])
     n_total = hpat.distributed_api.dist_reduce(n_local, np.int32(Reduce_Type.Sum.value))
 
     n_pes = hpat.distributed_api.get_size()