dmaengine: dmatest: move callback wait queue to thread context

Commit adfa543e ("dmatest: don't use set_freezable_with_signal()")
introduced a bug (that is in fact documented by the patch commit text)
that leaves behind a dangling pointer. Since the done_wait structure is
allocated on the stack, future invocations to the DMATEST can produce
undesirable results (e.g., corrupted spinlocks).

Commit a9df21e3 ("dmaengine: dmatest: warn user when dma test times
out") attempted to WARN the user that the stack was likely corrupted but
did not fix the actual issue.

This patch fixes the issue by pushing the wait queue and callback
structs into the the thread structure. If a failure occurs due to time,
dmaengine_terminate_all will force the callback to safely call
wake_up_all() without possibility of using a freed pointer.

Cc: stable@vger.kernel.org
Bug: https://bugzilla.kernel.org/show_bug.cgi?id=197605


Fixes: adfa543e ("dmatest: don't use set_freezable_with_signal()")
Reviewed-by: Sinan Kaya <okaya@codeaurora.org>
Suggested-by: Shunyong Yang <shunyong.yang@hxt-semitech.com>
Signed-off-by: Adam Wallis <awallis@codeaurora.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>