x86, 32-bit: Use generic sys_pipe()

As suggested by Al, it's better to use the generic sys_pipe() for ia32.

Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>