usb: typec_altmode: add a missing "@" at a kernel-doc parameter

Without that, the parameter is not properly parsed:
	include/linux/usb/typec_altmode.h:132: warning: Function parameter or member 'altmode' not described in 'typec_altmode_get_orientation'

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/70dc4c5d744cf1fe9a0efe6b85deaa0489628282.1656409369.git.mchehab@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>