dmaengine: update kerneldoc

Some of the kerneldoc comments in the dmaengine header describe
already removed structure members.  Remove them.

Also add a short description for dma_device->device_is_tx_complete.

Signed-off-by: Johannes Weiner <jw@emlix.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
1 file changed