leds-twl4030-pwm: fix another race

This is a race between twl4030_pwmled_work() reading led->new_brightness
vs twl4030_pwmled_brightness() writing to it. Probably needs a proper
lock, but we want twl4030_pwmled_brightness() to not block and assume
work items come from single queue and should not race each other.

diff --cc drivers/leds/leds-twl4030-pwm.c
Simple merge