In ems_usb_start() MAX_RX_URBS coherent buffers are allocated and
there is nothing, that frees them:

1) In callback function the urb is resubmitted and that's all
2) In disconnect function urbs are simply killed, but URB_FREE_BUFFER
   is not set (see ems_usb_start) and this flag cannot be used with
   coherent buffers.

So, all allocated buffers should be freed with usb_free_coherent()
explicitly.

Side note: This code looks like a copy-paste of other can drivers. The
same patch was applied to mcba_usb driver and it works nice with real
hardware. There is no change in functionality, only clean-up code for
coherent buffers.

Fixes: 702171ad ("ems_usb: Added support for EMS CPC-USB/ARM7 CAN/USB interface")
Link: https://lore.kernel.org/r/59aa9fbc9a8cbf9af2bbd2f61a659c480b415800.1627404470.git.paskripkin@gmail.com
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>