net: ethernet: ti: cpts: Handle error for clk_enable

As the potential failure of the clk_enable(),
it should be better to check it and return error
if fails.

Fixes: 8a2c9a5a

 ("net: ethernet: ti: cpts: rework initialization/deinitialization")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>