net: aquantia: fix warnings on endianness

fixes to remove sparse warnings:
sparse: sparse: cast to restricted __be64

Fixes: 04a18399 ("net: aquantia: implement data PTP datapath")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>