Added missing return to bli_thread_partition_2x2().

Details:
- Added a missing return statement to the body of an early case handling
  branch in bli_thread_partition_2x2(). This bug only affected cases
  where n_threads < 4, and even then, the code meant to handle cases
  where n_threads >= 4 executes and does the right thing, albeit using
  more CPU cycles than needed. Nonetheless, thanks to Kiran Varaganti
  for reporting this bug via issue #377.
- Whitespace changes to bli_thread.c (spaces -> tabs).

Change-Id: I2182be0911f76861dd14bec9b6bacb6c20c2725d

frame/thread/bli_thread.c

@@ -1062,6 +1062,8 @@ void bli_thread_partition_2x2
     {
         *nt1 = ( work1 >= work2 ? n_thread : 1 );
         *nt2 = ( work1 <  work2 ? n_thread : 1 );
+
+		return;
     }
 
     *nt1 = 1;