clk: sunxi: move "ahb_sdram" to protected clock list

With sunxi_gates clocks registered with clkdev, we can use the
protected clocks list to enable the "ahb_sdram" clock, instead
of looking for it and adding CLK_IGNORE_UNUSED inline in the
clock setup code.

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