HID: local function should be static

__usbhid_submit_report() is a local function wrapped by the exported
symbol usbhid_submit_report(). As such, it should be static.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc:  Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>