Introduce two structures for the (DMA address, length) combination instead
of using separate structure members for the DMA address and length. This
patch fixes several Coverity complaints about 'cur_dsd' being used to write
outside the bounds of structure members.

Cc: Himanshu Madhani <hmadhani@marvell.com>
Cc: Giridhar Malavali <gmalavali@marvell.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>