HID: usbhid: Repair a formatting issue in a struct description

Fixes the following W=1 kernel build warning(s):

 drivers/hid/usbhid/usbkbd.c:66: warning: bad line:                 should be on

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: message to <vojtech@ucw.cz>
Cc: linux-usb@vger.kernel.org
Cc: linux-input@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>