net: ethernet: ti: am65-cpsw-nuss: remove dead vid check in slave_add_vid()

net: ethernet: ti: am65-cpsw-nuss: remove dead vid check in slave_add_vid()

am65_cpsw_nuss_ndo_slave_add_vid() returns early at the top with:

     if (!netif_running(ndev) || !vid)
         return 0;

so vid is guaranteed to be non-zero in the rest of the function. The
subsequent

     if (!vid)
         unreg_mcast = port_mask;

is therefore unreachable. Drop the dead branch.

With that branch gone, unreg_mcast is only ever its initializer value
of zero, so drop the variable and pass 0 directly to
cpsw_ale_vlan_add_modify().

No functional change.

Found by Smatch.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/aS_lhMwppbDHoEcX@stanley.mountain
Signed-off-by: Alexander Vassilevski <oss@vassilevski.com>
Reviewed-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Link: https://patch.msgid.link/20260517220757.2679458-1-oss@vassilevski.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>