USB: HID: Steelseries SRW-S1 Add support for LEDs

This patch to the SRW-S1 driver adds support for the LED RPM
meter on the front of the device. The LEDs are controlled via
/sys/class/leds interface, with an individual control for each
of the 15 LEDs.

Signed-off-by: Simon Wood <simon@mungewell.org>
Tested-by: John Murphy <rosegardener@freeode.co.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>