net: bcmasp: Sanity check is off by one

A sanity check for OOB write is off by one leading to a false positive
when the array is full.

Fixes: 9b90aca9

 ("net: ethernet: bcmasp: fix possible OOB write in bcmasp_netfilt_get_all_active()")
Signed-off-by: Justin Chen <justin.chen@broadcom.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>