sanitize do_pipe_flags() callers in arch

* hpux_pipe() - no need to take BKL
* sys32_pipe() in arch/x86/ia32 and xtensa_pipe() in arch/xtensa -
	no need at all, since both functions are open-coded sys_pipe()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>