clk: sunxi-ng: a33: Set CLK_SET_RATE_PARENT for the GPU

In order to achieve all the rates asked by the GPU, we might need to change
the parent frequency.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>