staging: wilc1000: remove redundant result < 0 check

The check for result < 0 is redundant because at that point result
is always zero, hence we can remove this check and the netdev_err
message.

Detected by CoverityScan, CID#1357147 ("Logically Dead Code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>