clk: socfpga: arria10: convert to use clk_hw

As recommended by Stephen Boyd, convert the Arria10 clock driver to use
the clk_hw registration method.

Suggested-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lore.kernel.org/r/20210302214151.1333447-2-dinguyen@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>