TIOCGPTPEER is only used for unix98 PTYs, and we get a warning
when those are disabled:
drivers/tty/pty.c:466:12: error: 'pty_get_peer' defined but not used [-Werror=unused-function]
This moves the respective functions inside of the existing #ifdef.
Fixes: 54ebbfb16034 ("tty: add TIOCGPTPEER ioctl")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>