amd-xgbe: Add check to be sure amd-xgbe-phy driver is used

The amd-xgbe driver relies on the amd-xgbe-phy phylib driver. Add a
check to be sure that if any errors occur during probing of the
amd-xgbe-phy driver then the amd-xgbe driver returns an error.

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