leds: turn off regulator when brightness goes to 0

Signed-off-by: Guido Günther <guido.gunther@puri.sm>
2 jobs for mrs/lm3962x-power-off-reg in 46 minutes and 55 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Build
passed #234489
librem5
build:aarch64

00:29:52

passed #234490
librem5
build:deb

00:46:55