Test: correct an error in test_pipe_user_thread2thread().

In test_pipe_user_thread2thread(), what should be tested is
the pipe, which allocated with k_object_alloc(), rather than
"pipe" and "kpipe". That two pipes are already teseted in
test_pipe_thread2thread().

Signed-off-by: Steven Wang <steven.l.wang@linux.intel.com>
1 file changed