leds: sgm3140: Add missing timer cleanup and flash gpio control

Enabling strobe and then setting brightness to 0 causes the driver to enter
invalid state after strobe end timer fires. We should cancel strobe mode
resources when changing brightness (aka torch mode).

Fixes: cef8ec8c ("leds: add sgm3140 driver")
Signed-off-by: Ondrej Jirman <megi@xff.cz>
Link: https://lore.kernel.org/r/20240217191133.1757553-1-megi@xff.cz


Signed-off-by: Lee Jones <lee@kernel.org>