can: mcba_usb_start(): add missing urb->transfer_dma initialization

Yasushi reported, that his Microchip CAN Analyzer stopped working
since commit 91c0255 ("can: mcba_usb: fix memory leak in
mcba_usb"). The problem was in missing urb->transfer_dma
initialization.

In my previous patch to this driver I refactored mcba_usb_start() code
to avoid leaking usb coherent buffers. To archive it, I passed local
stack variable to usb_alloc_coherent() and then saved it to private
array to correctly free all coherent buffers on ->close() call. But I
forgot to initialize urb->transfer_dma with variable passed to
usb_alloc_coherent().

All of this was causing device to not work, since dma addr 0 is not
valid and following log can be found on bug report page, which points
exactly to problem described above.

| DMAR: [DMA Write] Request device [00:14.0] PASID ffffffff fault addr 0 [fault reason 05] PTE Write access is not set

Fixes: 91c0255 ("can: mcba_usb: fix memory leak in mcba_usb")
Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=990850
Link: https://lore.kernel.org/r/[email protected]
Cc: linux-stable <[email protected]>
Reported-by: Yasushi SHOJI <[email protected]>
Signed-off-by: Pavel Skripkin <[email protected]>
Tested-by: Yasushi SHOJI <[email protected]>
[mkl: fixed typos in commit message - thanks Yasushi SHOJI]
Signed-off-by: Marc Kleine-Budde <[email protected]>

drivers/net/can/usb/mcba_usb.c

@@ -653,6 +653,8 @@ static int mcba_usb_start(struct mcba_priv *priv)
 			break;
 		}
 
+		urb->transfer_dma = buf_dma;
+
 		usb_fill_bulk_urb(urb, priv->udev,
 				  usb_rcvbulkpipe(priv->udev, MCBA_USB_EP_IN),
 				  buf, MCBA_USB_RX_BUFF_SIZE,