clk: sunxi: make use of of_clk_parent_fill helper function

Use of_clk_parent_fill to fill in the parent clock names' array.

Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: "Emilio López" <emilio@elopez.com.ar>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>