octeon_ep: fix tx dma unmap len values in SG

Lengths of SG pointers are kept in the following order in
the SG entries in hardware.
 63      48|47     32|31     16|15       0
 -----------------------------------------
 |  Len 0  |  Len 1  |  Len 2  |  Len 3  |
 -----------------------------------------
 |                Ptr 0                  |
 -----------------------------------------
 |                Ptr 1                  |
 -----------------------------------------
 |                Ptr 2                  |
 -----------------------------------------
 |                Ptr 3                  |
 -----------------------------------------
Dma pointers have to be unmapped based on their
respective lengths given in this format.

Fixes: 37d79d05 ("octeon_ep: add Tx/Rx processing and interrupt support")
Signed-off-by: Shinas Rasheed <srasheed@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>