ethernet: aquantia: fix dma_mapping_error test

dma_mapping_error() returns 1 if there is an error and 0 if not.

Fixes: 018423e9

 ("net: ethernet: aquantia: Add ring support code")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>