ARM: dts: rockchip: Remove bogus 'i2s_clk_out' from rk3288-veyron-mickey

The rk3288-veyron-mickey device tree overrides the default "i2s" clock
settings to add the clock for "i2s_clk_out".

That clock is only present in the bindings downstream Chrome OS 3.14
tree.  Upstream the i2s port bindings doesn't specify that as a
possible clock.

Let's remove it.

NOTE: for other rk3288-veyron devices this clock is consumed by
'maxim,max98090'.  Presumably if this clock is needed for mickey it'll
need to be consumed by something similar.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>