Fix calculation of the index into TTY_LETTERS.  This only worked because sizeof(TTY_LETTERS) == sizeof(TTY_SUFFIX).
Fix calculation of the index into TTY_LETTERS.  This only worked
because sizeof(TTY_LETTERS) == sizeof(TTY_SUFFIX).

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars