usb: typec: stusb160x: fix an IS_ERR() vs NULL check in probe

The typec_register_port() function doesn't return NULL, it returns error
pointers.

Fixes: da0cb631 ("usb: typec: add support for STUSB160x Type-C controller family")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20201023114017.GE18329@kadam


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