dmaengine: tegra-apb: Clean up tasklet releasing

dmaengine: tegra-apb: Clean up tasklet releasing

There is no need to kill tasklet when driver's probe fails because tasklet
can't be scheduled at this time. It is also cleaner to kill tasklet on
channel's freeing rather than to kill it on driver's removal, otherwise
tasklet could perform a dummy execution after channel's releasing, which
isn't very nice.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20200209163356.6439-6-digetx@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>