staging: typec: tcpci: use IS_ERR() instead of PTR_ERR_OR_ZERO()

As tcpm_register_port() and tcpci_register_port() never return
NULL and NULL is not a success in this case, use IS_ERR() to check
the return value of both.

Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Li Jun <jun.li@nxp.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>