amd-xgbe: Resolve checkpatch warning about sscanf usage

Checkpatch issued a warning preferring to use kstrto<type> when
using a single variable sscanf.  Change the sscanf invocation to
a kstrtouint call.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>