arm64: dts: sprd: remove broken header inclusion

The added header inclusion broke the 'allmodconfig' build in
arm-soc, presumably since the file is added in a different tree:

In file included from arch/arm64/boot/dts/sprd/sp9860g-1h10.dts:11:0:
arch/arm64/boot/dts/sprd/sc9860.dtsi:10:10: fatal error: dt-bindings/clock/sprd,sc9860-clk.h: No such file or directory

It turns out we don't actually need to include it at all, so
I'm removing the line again to fix the build.

Fixes: 22f37a24

 ("arm64: dts: add clocks for SC9860")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>