tty: core: Refactor parameters for unset_locked_termios() helper

Add tty as parameter to unset_locked_termios() and extract former
parameters, termios and locked, as locals.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>