clk: add include guard to clk-conf.h

Add a header include guard just in case.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Link: https://lkml.kernel.org/r/20190820030536.1181-1-yamada.masahiro@socionext.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>