mlxsw: core: remove an unnecessary condition

We checked "err" on the lines before so we know it's zero here.

These cause a static checker warning because checking known things can
indicate a bug.  Maybe there is a missing assignment or we are checking
the wrong variable.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>