net: ethernet: ti: cpsw: remove clk var from priv

There is no need to hold link to clk, it's used only once
while probe.

Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>