greybus: legacy: fix a null pointer dereference

When gb_protocol_get() fails in legacy_connection_create(), we end up
bailing-out before assigning lc->connection and lc->protocol. Calling
legacy_connection_destroy() in that case results in a null pointer
dereference.

Check if lc->connection is not null before freeing it.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/legacy.c

@@ -148,6 +148,9 @@ static int legacy_connection_create(struct legacy_connection *lc,
 
 static void legacy_connection_destroy(struct legacy_connection *lc)
 {
+	if (!lc->connection)
+		return;
+
 	lc->connection->protocol = NULL;
 
 	gb_connection_destroy(lc->connection);