clk: core: add __init decoration for CLK_OF_DECLARE_DRIVER function

The new introduced macro CLK_OF_DECLARE_DRIVER is usually used to
declare clock driver init functions, which are mostly decorated with
__init.  Add __init decoration for CLK_OF_DECLARE_DRIVER function to
avoid causing section mismatch warnings on client clock drivers.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Fixes: c7296c51 ("clk: core: New macro CLK_OF_DECLARE_DRIVER")
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>