[PATCH] remove horrors with irix tty ioctls handling

Existing code in there (get_tty(), etc.) is both severely
racy *and* pointless: ioctls in question have Linux equivalents
and there's no need to play silly buggers in irix_ioctl() -
just need to replace arguments and, in case of TIOCGSID,
deal with API differences - Linux one expects pid_t __user *
while Irix one does unsigned long __user *.  BFD...

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