HID: Set Report ID properly for Output reports on the Control endpoint.

When I made commit 29129a98 ("HID: Send Report ID when numbered
reports are sent over the control endpoint"), I didn't account for *buf
not being the report ID anymore, as buf is incremented.

Signed-off-by: Alan Ott <alan@signal11.us>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>