net: au1000 eth: simplify logical expression

(a && a > 0) is equivalent to (a > 0).

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>