dma: mv_xor: Remove all callers of mv_xor_slot_cleanup()

In order to simplify the code, remove all the calls to the locked
mv_xor_slot_cleanup() and instead use the unlocked version only,

It's less error prone to have just one function, and require the caller
to ensure proper locking.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>