amd-xgbe: Fix sparse endian warnings

Change the types of the descriptor entries in the xgbe_ring_desc struct
from u32 to __le32 to fix endian warnings issued by sparse.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>