HID: hid-sony: report actual brightness value when reading LED

The Dualshock4 controller contains a RGB LED, which is enabled via
the '/sys/class/leds' interface. At present the driver only returns
whether each of the RGB LEDs is lit (ie not off), but no indication
of it's brightness.

This patch fixes the reading of the current brightnes so that it
returns the value (rather than just off=0, on=LED_FULL).

Tested on the DS4 and SixAxis (for compatibility).

Signed-off-by: Simon Wood <simon@mungewell.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>