net: openswitch: reuse the helper variable to improve the code readablity

In the function ovs_ct_limit_exit, there is already a helper vaibale
which could be reused to improve the readability, so i fix it in this
patch.

Signed-off-by: Zeng Tao <prime.zeng@hisilicon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>