arcnet: capmode: remove redundant assignment to pointer pkt

Pointer pkt is being initialized with a value that is never read
and pkt is being re-assigned a little later on. The assignment is
redundant and hence can be removed.

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