usb: image: mdc800: kill download URB on timeout

mdc800_device_read() submits download_urb and waits for completion.
If the timeout fires and the device has not responded, the function
returns without killing the URB, leaving it active.

A subsequent read() resubmits the same URB while it is still
in-flight, triggering the WARN in usb_submit_urb():

  "URB submitted while active"

Check the return value of wait_event_timeout() and kill the URB if
it indicates timeout, ensuring the URB is complete before its status
is inspected or the URB is resubmitted.

Similar to
- commit 372c93131998 ("USB: yurex: fix control-URB timeout handling")
- commit b98d5000c505 ("media: rc: iguanair: handle timeouts")

Signed-off-by: Ziyi Guo <n7l8m4@u.northwestern.edu>
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/20260209151937.2247202-1-n7l8m4@u.northwestern.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>