By making hid_is_usb() a non-inline function the lowlevel usbhid driver
does not have to be exported anymore.

Also mark the argument as const as it is not modified.
Signed-off-by: NThomas Weißschuh <linux@weissschuh.net>
Reviewed-by: NDavid Rheinsberg <david.rheinsberg@gmail.com>
Reviewed-by: NHans de Goede <hdegoede@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>