Documentation: ABI: led-trigger-pattern: Fix typos

  - Spelling s/brigntess/brightness/,
  - Double "use".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>