ARM: tegra: dma: Do not call complete callback on canceled requests

ARM: tegra: dma: Do not call complete callback on canceled requests

Calling the complete callback when a request is cancelled leads to
locking problems in the callback, which could be called from an IRQ
with no locks held, or from whatever context called
tegra_dma_dequeue_req.  Instead, expect the caller to handle the
now-cancelled request as needed.

Also removes tegra_dma_dequeue, since all users can be trivially
converted to tegra_dma_dequeue_req.

Change-Id: If699239c09c78d1cd3afa0eaad46535b1d401a24
Signed-off-by: Colin Cross <ccross@android.com>