clk: socfpga: remove clk_ops enable/disable methods

The enable/disable clock ops are already defined in the standard clock
ops, so we don't need to assign them.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lkml.kernel.org/r/20200512181647.5071-2-dinguyen@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>