Fixed int-to-packbuf_t conversion error (C++ only).

Details:
- Fixed an error that manifests only when using C++ (specifically,
  modern versions of g++) to compile drivers in 'test' (and likely most
  other application code that #includes blis.h. Thanks to Ajay Panyala
  for reporting this issue (#374).

frame/base/bli_mem.h

@@ -147,14 +147,7 @@ static void bli_mem_set_size( siz_t size, mem_t* mem )
 static void bli_mem_clear( mem_t* mem )
 {
 	bli_mem_set_buffer( NULL, mem );
-#ifdef __cplusplus
-	packbuf_t pb;
-	//C++ has more strong type checking. Using -1 will result in error
-	//Pass actual type instead
-	bli_mem_set_buf_type ( pb, mem );
-#else
 	bli_mem_set_buf_type( ( packbuf_t )-1, mem );
-#endif
 	bli_mem_set_pool( NULL, mem );
 	bli_mem_set_size( 0, mem );
 }