The test for BTUSB_DOWNLOADING must be after adding to the wait queue
and setting the TASK_INTERRUPTIBLE state. Otherwise the flag may get
cleared after we test for it and we end up getting a timeout since
schedule_timeout() waits for the full duration. This patch uses a
wait_on_bit_timeout() + wake_up_bit(). To perform the task both
race-free as well as in a much simpler way.

Since there's no global wait_on_bit_timeout() helper yet (even though
all the building blocks for it are in place) this patch creates a
temporary local btusb copy of it until the global one has made it to
upstream trees.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>