dmaengine: mv_xor_v2: kill the tasklets upon exit

The mv_xor_v2 driver uses a tasklet, initialized during the probe()
routine. However, it forgets to cleanup the tasklet using
tasklet_kill() function during the remove() routine, which this patch
fixes. This prevents the tasklet from potentially running after the
module has been removed.

Fixes: 19a340b1 ("dmaengine: mv_xor_v2: new driver")

Signed-off-by: Hanna Hawa <hannah@marvell.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>