greybus: use gbuf's destination cport id

If the buffer allocated in the ES1 alloc_gbuf_data() routine is for
outbound data, we are getting the destination CPort id from the
connection.  Switch to using the copy of the destination cport id
we now have in the gbuf instead.

Check for a valid CPort id there only if we're inserting it into
the buffer.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/es1-ap-usb.c

@@ -96,7 +96,6 @@ static void cport_out_callback(struct urb *urb);
 static int alloc_gbuf_data(struct gbuf *gbuf, unsigned int size,
 				gfp_t gfp_mask)
 {
-	struct gb_connection *connection = gbuf->operation->connection;
 	u32 cport_reserve = gbuf->dest_cport_id == CPORT_ID_BAD ? 0 : 1;
 	u8 *buffer;
 
@@ -118,20 +117,16 @@ static int alloc_gbuf_data(struct gbuf *gbuf, unsigned int size,
 	if (!buffer)
 		return -ENOMEM;
 
-	/*
-	 * we will encode the cport number in the first byte of the buffer, so
-	 * set the second byte to be the "transfer buffer"
-	 */
-	if (connection->interface_cport_id > (u16)U8_MAX) {
-		pr_err("gbuf->interface_cport_id (%hd) is out of range!\n",
-			connection->interface_cport_id);
-		kfree(buffer);
-		return -EINVAL;
-	}
-
 	/* Insert the cport id for outbound buffers */
-	if (cport_reserve)
-		*buffer++ = connection->interface_cport_id;
+	if (cport_reserve) {
+		if (gbuf->dest_cport_id > (u16)U8_MAX) {
+			pr_err("gbuf->dest_cport_id (%hd) is out of range!\n",
+				gbuf->dest_cport_id);
+			kfree(buffer);
+			return -EINVAL;
+		}
+		*buffer++ = gbuf->dest_cport_id;
+	}
 	gbuf->transfer_buffer = buffer;
 	gbuf->transfer_buffer_length = size;