platform/chrome: cros_ec_typec: Rename port altmode array

Rename "p_altmode" to "port_altmode" which is a less ambiguous name for
the port_altmode struct array.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20220712210318.2671292-1-pmalani@chromium.org