clk: scpi: mark scpi_clk_match as maybe unused

clk: scpi: mark scpi_clk_match as maybe unused

The scpi_clk_match (struct of_device_id) is referenced only with
CONFIG_OF builds thus mark it as __maybe_unused:

    drivers/clk/clk-scpi.c:132:34: warning:
        ‘scpi_clk_match’ defined but not used [-Wunused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201103162435.13689-8-krzk@kernel.org
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>