leds: leds-lp3944, fix "sparse" warning "mixing different enum types"

Fix a warning from "sparse":

drivers/leds/leds-lp3944.c:292:23: warning: mixing different enum types
drivers/leds/leds-lp3944.c:292:23:     int enum led_brightness  versus
drivers/leds/leds-lp3944.c:292:23:     int enum lp3944_status

Keeping track of LP3944_LED_STATUS_OFF and LP3944_LED_STATUS_ON only in
lp3944_led_set_brightness() is OK, as the handling of DIM (blinking)
mode[s] is in lp3944_led_set_blink().

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>