ethernet: amd: use PTR_RET instead of IS_ERR + PTR_ERR

This uses PTR_RET instead of IS_ERR and PTR_ERR in order to increase
readability.

Signed-off-by: Silviu-Mihai Popescu <silviupopescu1990@gmail.com>
Acked-by: &lt;Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: David S. Miller <davem@davemloft.net>