ister is 16-bits so ->dmacount should
be unsigned and 16-bit as well.  Also modify ->desccount to maintain
alignment.

This was never a problem in practice because we never compared dmacount
values, but this is a bug waiting to happen.

Signed-off-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

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