usb: typec: fix dereference before null check on adev

Pointer adev is being dereferenced before it is being sanity
checked with a null pointer check, hence it is possible for
a null pointer dereference to occur.  Fix this by dereferencing
adev only once it is null checked.

Detected by CoverityScan, CID#1471598 ("Dereference before null check")

Fixes: 8a37d87d72f0 ("usb: typec: Bus type for alternate modes")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/bus.c

@@ -51,7 +51,7 @@ static int typec_altmode_set_state(struct typec_altmode *adev, int state)
 int typec_altmode_notify(struct typec_altmode *adev,
 			 unsigned long conf, void *data)
 {
-	bool is_port = is_typec_port(adev->dev.parent);
+	bool is_port;
 	struct altmode *altmode;
 	struct altmode *partner;
 	int ret;
@@ -64,6 +64,7 @@ int typec_altmode_notify(struct typec_altmode *adev,
 	if (!altmode->partner)
 		return -ENODEV;
 
+	is_port = is_typec_port(adev->dev.parent);
 	partner = altmode->partner;
 
 	ret = typec_altmode_set_mux(is_port ? altmode : partner, (u8)conf);