wimax: i2400: fix memory leak

[ Upstream commit 2507e6ab7a9a440773be476141a255934468c5ef ]

In i2400m_op_rfkill_sw_toggle cmd buffer should be released along with
skb response.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>