Fix potential buffer overflow in case the device ID did not end in semicolon.
Also might fail to negotiate back to IEEE1284_MODE_COMPAT in case of failure.
parport_device_id did not return what Documentation/parport-lowlevel.txt said,
so I changed it to match it.

Determining device ID length is overly complicated, but Tim Waugh recalled on
linux-parport seeing some buggy device that might need it.
Signed-off-by: Marko Kohtala <marko.kohtala@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>