HID: playstation: DS4: Fix LED blinking

There was no way to disable blinking once enabled.
Disable it on brightness = 0, as per the Linux LED spec.

The driver reports back the values it sends to the controller, but they
need to be scaled back to milliseconds. Setting the LED blinking via
sysfs works as expected now.

Signed-off-by: Max Staudt <max@enpas.org>
Signed-off-by: Jiri Kosina <jkosina@suse.com>