HID: steelseries: arctis_1_battery_request[] should be static

arctis_1_battery_request[] is not used outside of this module, and as
such should be static.

Fixes: a0c76896 ("HID: steelseries: Add support for Arctis 1 XBox")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>