leds: bcm6328: simplify duplicated unlock in bcm6328_blink_set

Instead of duplicating the unlock we can store the return value and use a
single unlock before returning that value, which simplifies the code.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>