dpaa_eth: fix SG mapping

[ Upstream commit 120d75ecf043044554abbba8507f6d22e4715beb ]

An issue in the code mapping the skb fragments into
scatter-gather frames was evidentiated by netperf
TCP_SENDFILE tests. The size was set wrong for all
fragments but the first, affecting the transmission
of any skb with more than one fragment.

Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>