dpaa2-eth: allocate a fragment already aligned

Instead of allocating memory and then manually aligning it to the
desired value use napi_alloc_frag_align() directly to streamline the
process.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>