ARM: dts: sun9i: Add clock-indices property for bus gate clocks

of_clk_get_parent_name() uses the clock-indices property to resolve
clock phandle arguments in case that the argument index does not
match the clock-output-names sequence.

This is the case on sunxi, where we use the actual bit index as the
argument to the phandle. Add the clock-indices property so that
of_clk_get_parent_name() resolves the names correctly.

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