dmaengine: apple-admac: Fix 'current_tx' not getting freed

In the Linux kernel, the following vulnerability has been resolved:

dmaengine: apple-admac: Fix 'current_tx' not getting freed

In terminate_all we should queue up all submitted descriptors to be

freed. We do that for the content of the 'issued' and 'submitted' lists,

but the 'current_tx' descriptor falls through the cracks as it's

removed from the 'issued' list once it gets assigned to be the current

descriptor. Explicitly queue up freeing of the 'current_tx' descriptor

to address a memory leak that is otherwise present.