tty: fix spelling mistake

Fix typo: "tigger" --> "trigger"

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Link: https://lore.kernel.org/r/20200609160249.31329-1-f.suligoi@asem.it
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>