can: mcba_usb: fix memory leak in mcba_usb

In the Linux kernel, the following vulnerability has been resolved:

can: mcba_usb: fix memory leak in mcba_usb

Syzbot reported memory leak in SocketCAN driver for Microchip CAN BUS

Analyzer Tool. The problem was in unfreed usb_coherent.

In mcba_usb_start() 20 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 mcba_usb_start) and this flag cannot be used with

coherent buffers.

Fail log:

| [ 1354.053291][ T8413] mcba_usb 1-1:0.0 can0: device disconnected

| [ 1367.059384][ T8420] kmemleak: 20 new suspected memory leaks (see /sys/kernel/debug/kmem)

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

explicitly

NOTE:

The same pattern for allocating and freeing coherent buffers

is used in drivers/net/can/usb/kvaser_usb/kvaser_usb_core.c