usb: typec: ucsi: Only check the contract if there is a connection

The driver must make sure there is an actual connection
before checking details about the USB Power Delivery
contract. Those details are not valid unless there is a
connection.

This fixes NULL pointer dereference that is caused by an
attempt to register bogus partner alternate mode that the
firmware on some platform may report before the actual
connection.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215117
Fixes: 6cbe4b2d ("usb: typec: ucsi: Check the partner alt modes always if there is PD contract")
Reported-by: Chris Hixon <linux-kernel-bugs@hixontech.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/eb34f98f-00ef-3238-2daa-80481116035d@leemhuis.info/
Link: https://lore.kernel.org/r/20211221140352.45501-1-heikki.krogerus@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/ucsi/ucsi.c

@@ -1150,7 +1150,9 @@ static int ucsi_register_port(struct ucsi *ucsi, int index)
 		ret = 0;
 	}
 
-	if (UCSI_CONSTAT_PWR_OPMODE(con->status.flags) == UCSI_CONSTAT_PWR_OPMODE_PD) {
+	if (con->partner &&
+	    UCSI_CONSTAT_PWR_OPMODE(con->status.flags) ==
+	    UCSI_CONSTAT_PWR_OPMODE_PD) {
 		ucsi_get_src_pdos(con);
 		ucsi_check_altmodes(con);
 	}