net: ethernet: sun: remove redundant assignment to variable err

The variable err is being assigned with a value that is never
read and it is being updated in the next statement with a new value.
The assignment is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>